UNIVERSITY  OF  CALIFORNIA 

MEDICAL  CENTER  LIBRARY 

SAN  FRANCISCO 


Gift  of 


Or.  Howard  L.  Mawdsley 


ANATOMY  AND  PHYSIOLOGY 
FOR  NURSES 


THE  MACMILLAN  COMPANY 

NEW  YORK    •    BOSTON    •    CHICAGO  •    DALLAS 
ATLANTA   •    SAN    FRANCISCO 

MACMILLAN   &   CO.,  LIMITED 

LONDON   •    BOMBAY   •    CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


TEXT-BOOK 


OF 


ANATOMY  AND  PHYSIOLOGY 

FOR  NURSES 


BY 
DIANA    CLIFFORD  fKIMBER 

GRADUATE    OF    BELLEVUE    TRAINING    SCHOOL^   FORMERLY    ASSISTANT 

SUPERINTENDENT    NEW    YORK     CITY    TRAINING     SCHOOL    FOR 

NURSES,     BLACKWELLS     ISLAND,     N.Y.   ;      FORMERLY 

ASSISTANT    SUPERINTENDENT    ILLINOIS 

TRAINING   SCHOOL,  CHICAGO,    ILL. 

AND 

CAROLYN  E.  GRAY,  B.Sc.(ucntSay),  R.N. 


FIFTH  EDITION,   REVISED 


gorfc 

THE   MACMILLAN   COMPANY 

1919 

f-     Q,     1C 

Att  rights1  ri 

1  Q  c  r  -' 

JL    SLf   ^     ^    ^    ^ 


COPYRIGHT,  1893, 

BY  MACMILLAN  AND  CO. 

COPYRIGHT,  1902,  1909,  1914,  1918, 

BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  September,  1894, 


Nortoooti 

J.  S.  Cushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE   TO   THE   FIFTH   EDITION 

IT  is  now  a  quarter  of  a  century  since  the  appearance  of  the 
first  edition  of  this  text-book  which  grew  out  of  Miss  Kimber's 
own  experience  in  the  classroom  and  which  has  always  repre- 
sented the  work  of  a  nurse  for  nurses.  Only  one  who  has  worked 
in  nurse-training  schools  can  appreciate  the  peculiar  disadvantages 
under  which  the  nurse  instructor  works,  because  of  the  varying 
standards  of  admission,  hours  of  duty,  inadequate  equipment, 
meagre  libraries,  etc.  We  believe  that  in  nursing,  as  in  medicine, 
our  most  helpful  books  must  be  produced  within  the  profession 
because  one  who  has  travelled  each  step  of  the  way,  as  pupil, 
instructor,  and  administrator,  has  a  more  complete  understanding 
of  the  needs  of  nurses  than  can  possibly  be  gained  in  a  less  intimate 
participation  in  the  work. 

In  this  revision  the  basic  importance  of  physiology,  in  the  train- 
ing and  education  of  the  nurse,  has  been  constantly  borne  in 
mind.  This  subject  must  form  the  groundwork  for  the  study  of 
hygiene,  dietetics,  materia  medica,  and  all  pathological  conditions, 
as  well  as  for  the  intelligent  practice  of  nursing  methods.  Enough 
anatomy  is  given  to  make  the  physiology  intelligible,  for  we  must 
understand  the  plan  or  organization  of  the  body  before  we  can 
appreciate  its  functioning. 

The  study  of  physics  and  chemistry  should  precede  that  of 
anatomy  and  physiology.  When  this  is  not  possible,  the  best 
compromise  is  to  have  chemistry  a  parallel  course.  Physiology, 
being  a  constantly  growing  subject,  we  cannot  expect  to  teach  final 
truth.  If  this  book  raises  many  more  questions  than  it  answers, 
it  will  have  served  its  purpose,  because  to  arouse  interest,  stimu- 
late curiosity  and  inquiry  are  the  main  objects  of  teaching. 

In  a  cultivation  of  the  scientific  habit  of  thought,  the  laboratory 
method  is  invaluable.  We  do  not  expect  the  student  to  make 


vi  PREFACE   TO   THE   FIFTH   EDITION 

new  discoveries,  but   she  can  be  shown   how  the  discoveries  of 
others  have  been  brought  about. 

Free  use  should  be  made  of  the  reference  library  and  this  should 
be  adequate  and  up-to-date. 

Blackboard  drawings  are  invaluable.  Models  and  charts  are 
useful,  but  nothing  takes  the  place  of  the  actual  specimen  which 
can  be  handled  and  dissected. 

The  aim  of  this  book  is  to  describe  in  as  simple  a  manner  as 
possible  the  phenomena  of  life,  and  the  principal  conclusions 
which  have  been  reached  as  to  their  interdependence  and  causes. 

The  gratifying  approval  which  previous  editions  have  received 
has  made  it  seem  unwise  to  attempt  any  change  in  the  order  of 
the  chapters.  This  seems  of  minor  importance  since  every  teacher 
will  wish  to  follow  her  own  method  in  teaching,  taking  the  systems 
in  such  order  as  seems  to  her  most  reasonable. 

I  have  had  the  advantage,  as  formerly,  of  the  help  and  advice 
of  many  fellow-workers  in  the  training  schools,  and  to  them  I 
extend  my  thanks.  I  am  specially  indebted  to  Caroline  E.  Stack- 
pole,  M.A.,  Instructor  in  Biology,  Teachers  College,  for  reading 
and  criticising  my  manuscript ;  to  Robert  M.  Lovett,  M.D.,  of 
Boston,  for  valuable  assistance  with  the  chapter  on  muscles ;  to 
Helen  L.  Redfern,  R.N.,  for  assistance  with  the  illustrations,  and 
to  Mabelle  S.  Welsh,  R.N.,  for  assistance  in  proof-reading  and  for 
making  the  index. 

I  am  also  indebted  to  the  authors  whose  works  I  have  con- 
sulted, and  to  the  various  publishers  who  have  granted  me  per- 
mission to  use  illustrations  from  their  books. 

C.   E.   G. 


TABLE   OF   CONTENTS 

CHAPTER  PAGE 

I.     Explanations  and  Definitions  of  Some  Chemical  and  Physical 

Terms 3 

II.     Definitions.  —  Cavities  of  the  Human  Body     ....       13 

III.  Cells,  Tissues,  Organs,  and  Systems.  —  Epithelial  Tissue.  — 

Nerve  Tissue 20 

IV.  Connective    Tissues :     Areolar,    Fibrous,    Elastic,    Adipose, 

Reticular,  Neuroglia,  Cartilage,  Bone 44 

V.  The  Skeleton.  —  Classification  of  Bones ;  Divisions  of  the 
Skeleton ;  Bones  of  the  Cranium ;  Bones  of  the  Face ;  Bones 
of  the  Trunk ;  Bones  of  the  Upper  Extremities ;  Bones  of 

the  Lower  Extremities 60 

VI.     Joints  or  Articulations .         .90 

VII.     Muscular    Tissue :     Classification ;     Functionally    Important 

Skeletal  Muscles 97 

VIII.     Special  Membranes  and  Glands 140 

IX.     Vascular  System  :  The  Blood;  The  Clotting  of  Blood ;  Lymph     154 
X.     The  Blood  Vascular  System,  and  the  Lymph  Vascular  System     173 
XI.     The  Vascular  System  Continued  :   Arteries ;   Pulmonary  Sys- 
tem;   General  System;    Veins;    Supplementary  Channel, 

and  Portal  System 197 

XII.     The  Vascular  System  Continued:    The  General  Circulation; 

Blood  Pressure;    The  Pulse;    Lymph;    Foetal  Circulation     228 

XIII.  Respiratory   System  :     Nose ;    Larynx ;     Trachea ;     Bronchi ; 

Lungs.  —  Respiration ;     Abnormal    Types    of    Respiration. 
—  Modified  Respiratory  Movements 247 

XIV.  The  Digestive    System :     Alimentary    Canal    and    Accessory 

Organs 271 

XV.     Food.  —  Digestive  Processes ;    Changes  the  Food  Undergoes 
in    the    Mouth,    Stomach,    Small    and    Large    Intestines; 

Absorption 304 

XVI.     General  Metabolism  ;   Metabolism  of  Carbohydrates ;   Metab- 
olism of  Fats ;   Metabolism  of  Proteins.  —  Ductless  Glands     334 
XVII.     Waste    Products;     Excretory    Organs;     Description    of    the 

Organs  Constituting  the  Urinary  System  ;  Urine  .     355 

XVIII.     The  Skin ;  Appendages  of  the  Skin.  —  Body  Heat ;  Regulation 

of  Heat.     Variations  in  Temperature    .....     376 

XIX.     The  Nervous  System         ...  ....     395 

XX.     Internal  and  External  Senses  :  Taste,  Smell,  Hearing,  and  Sight     429 
XXI.     The  Organs  of  Generation  :   Physiology  of  Reproduction          .     463 

GLOSSARY 491 

INDEX 509 

yii 


ANATOMY  AND   PHYSIOLOGY 
FOR  NURSES 


CHAPTER  I 

EXPLANATIONS    AND    DEFINITIONS    OF    SOME    CHEMICAL   AND 
PHYSICAL  TERMS 

AN  intelligent  discussion  of  the  various  functions  of  the  human 
body  cannot  be  given  without  some  elementary  considerations  in 
the  field  of  chemistry  and  its  intimately  related  science  of  physics. 
Probably  the  briefest  method  for  presenting  the  essential  points 
is  in  the  way  of  definitions  with  accompanying  illustrations,  and 
explanations  where  necessary. 

THE  PHYSICAL  SCIENCES 

1.  Physics  deals  with  mechanics,  heat,  light,  sound,  and  elec- 
tricity, and  their  relations  to  matter. 

2.  Chemistry  deals  with  change  in  the  composition  of  matter, 
the  energy  change  involved  therein,  and  the  principles  controlling 
chemical  change. 

MATTER 

1.  Defined.  —  Matter  is  usually  defined  as  anything  that  oc- 
cupies space,  and  possesses  weight,  as  wood,  air,  water. 

2.  Forms  in  which  matter  exists. 

Elements.  —  An  element  is  a  substance  which  cannot  be  sepa- 
rated into  more  simple  substances  by  any  means  known  to  science 
at  present.  Elements  are  supposed  to  be  made  up  of  atoms  which 
are  alike  for  the  same  element  and  cannot  be  divided. 

There  are  about  eighty  of  these  elements,  less  than  half  of 
which  are  well  known.  Some  of  the  most  common  are  carbon, 
iron,  sulphur,  mercury,  and  oxygen. 

Compounds.  —  A  compound  is  a  substance  which  can  be  sepa- 
rated into  simpler  substances.  Compounds  are  supposed  to  be 
made  up  of  molecules  which  are  composed  of  groups  of  atoms. 
Molecules  are  alike  for  the  same  compound  and  can  be  divided, 

3 


4  ANATOMY  AND   PHYSIOLOGY  [CHAP.  I 

giving  elements  or  simpler  compounds.  For  example,  water  is 
composed  of  hydrogen  and  oxygen,  each  molecule  having  in  it 
two  hydrogen  atoms  and  one  oxygen  atom  (H2O) ;  when  sepa- 
rated, water  gives  the  two  elements  hydrogen  and  oxygen.  Again, 
sugar  is  composed  of  hydrogen,  carbon,  and  oxygen,  each  mole- 
cule having  in  it  twelve  atoms  of  carbon,  twenty-two  atoms  of 
hydrogen,  and  eleven  atoms  of  oxygen  (C^H^On) ;  when  sepa- 
rated it  gives  several  compounds  with  simpler  molecules,  as  car- 
bon dioxide  (CO2),  water  (H2O),  methane  (CH4),  etc. 

Mixtures.  —  A  mixture  can  be  made  up  of  either  or  both  ele- 
ments and  compounds.  These  can  often  be  separated  by  simple 
physical  means,  as  filtration  or  evaporation.  Milk  is  a  mixture  of 
several  compounds,  —  water,  cream,  proteins,  sugar,  and  salts. 
The  cream  can  be  separated  by  allowing  the  milk  to  stand,  when 
it  will  rise  to  the  top,  and  can  be  skimmed  off.  Salt  solution  is 
a  mixture  of  the  compounds,  salt  and  water.  They  can  be  sepa- 
rated by  evaporating  the  water.  Air  is  a  mixture  of  compounds 
and  elements,  carbon  dioxide  (compound),  nitrogen  and  oxygen 
(elements).  They  cannot  be  separated  by  any  simple  means. 

3.   Matter  undergoes  changes. 

Physical  change. — When  matter  has  been  subjected  to  a 
change  which  does  not  affect  the  composition  of  the  matter,  the 
change  is  said  to  be  a  physical  one  only.  The  following  are 
given  by  way  of  illustration  :  — 

Water  can  solidify  (freeze)  or  it  can  vaporize ;  whether  it  exists 
in  the  state  of  a  solid,  a  liquid,  or  a  gas,  depends  upon  the  tempera- 
ture, but  the  composition  in  all  these  states  is  identical.  Sugar 
melts,  but  the  solid  sugar  and  the  liquid  sugar  are  exactly  the 
same  in  composition ;  the  change  is  only  one  in  physical  state. 

Other  physical  changes  besides  change  in  physical  state  are, 
change  in  size,  position,  magnetic  or  electric  condition,  and  change 
in  temperature. 

Chemical  change.  —  When  matter  undergoes  a  change  in  com- 
position, it  is  said  to  have  undergone  a  chemical  change.  The 
following  are  illustrations :  when  an  electric  current  is  passed 
through  water,  the  water  is  separated  into  two  distinct  substances, 
hydrogen  and  oxygen.  In  this  case  we  start  with  a  single  com- 
pound (water)  of  definite  composition,  and  as  a  result  of  the 
change,  obtain  two  different  substances  (oxygen  and  hydrogen). 


CHAP.  I]    EXPLANATIONS   AND  DEFINITIONS  5 

Again,  in  a  bar  of  iron  there  is  nothing  but  the  element  iron, 
but  if  it  is  left  exposed  to  the  air,  it  is  converted  into  a  red  solid 
which  has  iron  and  oxygen  in  it,  the  iron  having  combined  with 
some  of  the  oxygen  from  the  air.  The  iron  and  the  iron  rust  are 
evidently  different  in  composition. 

ELEMENTS  FOUND  IN  THE  BODY 

The  elements  found  in  the  body  are :  — 
Carbon,  13.5  (C) 


form  97  per  cent 
of  total 
weight  of  body. 


Hydrogen,  9.1             (H) 

Nitrogen,  2.5             (N) 

Oxygen,  72.0  (0) 

"Sulphur,  (S) 

Phosphorus,  (P) 

^Fluorine,  (F) 

Chlorine,  (Cl) 

Iodine,  (I) 

Silicon,  (Si) 

Sodium,  (Na) 

Potassium,  (K) 

Calcium,  (Ca) 

Magnesium,  (Mg) 

Lithium,  .     (Li) 

Iron,  (Fe) 

Manganese,  (Mn) 

Copper,  (Cu) 

Lead,  (Pb) 

These  elements  are  not,  of  course,  found  uncombined  in  the 
body,  but  rather  combined,  usually  in  the  form  of  rather  complex- 
compounds.  Protoplasm,  for  instance,  is  a  compound  of  carbon, 
hydrogen,  nitrogen,  oxygen,  and  phosphorus. 

ORGANIC  AND  INORGANIC  COMPOUNDS 

The  distinction  between  organic  and  inorganic  compounds 
dates  back  to  an  early  period,  when  there  was  a  belief  that  certain 
compounds  of  carbon  found  in  living  organisms  could  only  be  built 
up  through  the  agency  of  a  vital  force  possessed  by  the  organism, 
which  prevented  their  being  synthesized  in  the  chemical  laboratory. 
In  distinguishing  such  they  were  spoken  of  as  organic  compounds. 
However,  when  urea,  one  of  these  substances,  was  prepared  in 


6  ANATOMY  AND   PHYSIOLOGY  [CHAP.  I 

the  laboratory,  this  theory  was  abandoned,  but  the  distinctive 
terms  organic  and  inorganic  persisted.  Under  the  present  classi- 
fication organic  compounds  are  compounds  that  contain  carbon. 

Because  of  the  fact  that  there  are  numerous  carbon  compounds  and 
also  because  many  of  these  can  be  grouped  into  classes  with  well-defined 
characteristics,  the  study  of  the  carbon  compounds  has  become  a  separate 
phase  of  the  general  study  of  chemistry  and  is  called  organ's-  chemistry. 

SOME  CHEMICAL  TERMS 

Atom.  —  An  atom  is  the  smallest  part  into  which  an  element 
can  be  divided.  Atoms  are  alike  for  the  same  element,  but 
different  for  different  elements. 

Molecule.  —  A  molecule  is  a  group  of  atoms  in  chemical  com- 
bination. Compounds  are  made  up  of  multitudes  of  molecules, 
all  of  which  are  alike  for  the  same  compound. 

Chemical  formula.  —  A  chemical  formula  is  a  simple  means 
for  representing  the  composition  of  the  molecule.  Symbols  are 
made  use  of  to  represent  the  elements  and  small  subscript  figures 
to  represent  the  number  of  atoms  of  the  respective  elements. 
For  example,  the  formula  for  the  sulphuric  acid  molecule  (H2SO4) 
shows  it  to  be  made  up  of  two  atoms  of  hydrogen,  one  atom  of 
sulphur,  and  four  atoms  of  oxygen;  the  formula  for  the  sodium 
chloride  molecule  (NaCl)  shows  it  to  be  made  up  of  one  atom  of 
sodium  and  one  of  chlorine. 

Chemical  equation.  —  A  chemical  equation  is  a  simple  means 
for  representing  the  matter  change  that  takes  place  in  a  chemical 
action.  When  carbon  burns  it  combine*  w?th  oxygen  to  form 
carbon  dioxide.  The  equation  that  expresses  this, 

C 


tells  that  during  the  process  of  combination,  one  atom  of  carbon 
combines  with  one  molecule  of  oxygen  (composed  of  two  atoms)  to 
give  one  molecule  of  carbon  dioxide.  In  the  action  of  sodium 
hydroxide  with  hydrochloric  acid,  water  and  sodium  chloride  are 
formed.  The  equation  to  represent  this, 

NaOH  -f  HCl-*-H2O  +  NaCl, 

shows  that  one  molecule  of  sodium  hydroxide  reacts  with  one  mole- 
cule of  hydrochloric  acid  to  give  one  molecule  of  water  and  nna 
molecule  of  sodium  chloride. 


CHAP.  I]     EXPLANATIONS   AND   DEFINITIONS  7 

Oxide.  —  An  oxide  is  a  compound  in  which  another  element 
is  in  combination  with  oxygen,  as  water  (H2O),  carbon  dioxide 
(€02),  sulphur  dioxide  (802),  and  iron  oxide  (Fe2O3). 

Acid  oxide. — An  acid  oxide  (or  acid  anhydride)  is  an  oxide 
of  a  non-metal  which  in  combination  with  water  will  form  an 
acid,  as  carbon  dioxide  and  sulphur  dioxide,  shown  in  the  follow- 

inS :  ~  C02  +  H20->-H2C03  (carbonic  acid), 

SO3  +  H2O-^H2SO4  (sulphuric  acid). 

Basic  oxide.  —  A  basic  oxide  (or  basic  anhydride)  is  an  oxide 
of  a  metal  which  in  combination  with  water  will  give  a  base, 
as  calcium  oxide  (CaO)  and  sodium  oxide  (Na^O),  shown  in  the 
following :  — 

CaO  +  H2O->-Ca(OH)2  (calcium  hydroxide), 
Na^O  +  H2O>-2  NaOH  (sodium  hydroxide). 

Ion.  —  An  ion  is  an  atom  or  group  of  atoms  charged  with  elec- 
tricity. 

Acid.  —  An  acid  is  a  substance,  containing  hydrogen  and  an 
acid  radical,  which  dissolved  in  water  or  other  dissociating  liquid 
produces  hydrogen  ions.  The  acid  radical  must  contain  a  non- 
metal  and  may  contain  oxygen.  Examples  are  hydrochloric  acid 
(HC1),  sulphuric  acid  (H2SO4),  carbonic  acid  (H2CO3),  hydro- 
bromic  acid  (HBr),  nitric  acid  (HNO3). 

Base.  —  A  base  is  a  substance  which  contains  a  metal  and  the 
hydroxyl  (OH)  radical.  Examples  are  sodium  hydroxide  (NaOH) 
and  calcium  hydroxide  (Ca(OH)2).  One  exception 'to  this  is 
ammonium  hydroxide  (NH4OH),  which  contains  the  ammonium 
radical  (NH4)  instead  of  a  metal. 

The  alkalies  are  the  bases  of  sodium,  potassium,  and  ammonium ; 
they  give  very  strong  basic  action. 

Both  acids  and  bases  give  distinctive  characteristic  actions. 

Salt.  —  A  salt  is  a  substance  containing  the  metal  from  a  base 
and  the  acid  radical  from  an  acid.  Salts  may  be  obtained  by  the 
neutralization  of  an  acid  by  a  base,  the  characteristic  hydrogen  of 
the  acid  combining  with  the  characteristic  hydroxyl  of  the  base 
to  form  water,  leaving  the  salt  as  shown  in  the  following :  — 

Base         +  Acid   WVater  +  Salt 

NaOH      +  HC1    ->-H20     +  NaCl  (sodium  chloride), 

Ca(OH)2  +  H2SO4-^2H2O    +  CaSO4  (calcium  sulphate). 


8  ANATOMY  AND   PHYSIOLOGY  [CHAP.  I 

SOME  GENERAL  CHEMICAL  ACTIONS 

Oxidation.  —  Oxidation  is  the  process  in  which  the  element 
oxygen  combines  chemically  with  another  substance,  heat  being 
evolved  in  the  process.  The  heat  evolved  may  not  be  perceptible 
unless  the  oxidation  takes  place  rapidly,  as  in  the  burning  of  gas, 
wood,  coal,  etc.  If  the  substance  combines  slowly  with  oxygen, 
heat  may  be  imperceptible;  for  example,  iron  allowed  to  lie  in 
moist  air  is  covered  with  rust  due  to  the  union  of  the  iron  and 
oxygen.  Also  in  our  bodies  some  of  the  carbon  in  the  cells  unites 
with  oxygen,  and  thus  the  temperature  of  the  body  is  kept  up.  It 
is  for  this  reason  that  oxygen  must  be  taken  into  the  body,  which  is 
accomplished  by  the  act  of  breathing.  (See  page  258.) 

Neutralization.  —  Neutralization  is  the  process  that  takes  place 
in  the  action  of  an  acid  with  a  base.  Water  and  a  salt  are  the 
products  of  the  reaction.  (See  Salt.) 

Hydrolysis.  —  Hydrolysis  can  be  defined  as  the  chemical  change 
that  takes  place  when  a  compound  in  its  action  with  water  splits 
into  two  other  compounds,  fixing  the  elements  of  water  in  the 
process.  The  action  of  water  with  some  salts,  also  the  formation 
of  glucose  and  fructose  from  cane  sugar,  may  be  given  as  ex- 
amples, as  represented  in  the  following  reaction  equations :  - 

(Sodium  carbonate)  (Sodium  hydroxide)       (Carbonic  acid) 

Na2C03    +  2H2O-^2NaOH         +    H2CO3, 

(Cane  sugar)  (Fructose)  (Glucose) 

C12H22On  +  H20    ->•  C6H12O6         +    C6H1206. 

Hydration.  —  Hydration  is  the  process  by  which  water  enters 
into  direct  combination  with  another  compound  to  form  a  single 
compound  which  is  called  a  hydrate.  As  examples  might  be 
given,  sulphuric  acid  (H2SO4)  as  a  hydrate  of  sulphur  trioxide 
(SO3),  calcium  hydroxide  (Ca(OH)2)  as  a  hydrate  of  calcium  oxide 
(CaO),  and  crystalline  copper  sulphate  (CuSO4  .  5  H2O)  as  a  hy- 
drate of  anhydrous  copper  sulphate  (CuSO4).  The  formation  of 
these  hydrates  in  the  process  of  hydration  is  represented  in  the 

following:--    Anhydrous 

substances  Hydrates 

SO,       +  II20    +  H2S04 
CaO     +  II2O     :£  Ca(OH)2 
CuSO4  +  5  H2O  ±  CuSO4 .  5  H2O. 


CHAP.  I]     EXPLANATIONS   AND   DEFINITIONS  9 

The  reverse  process  by  which  a  compound  is  split  up  into  water 
and  an  anhydrous  compound  is  called  dehydration.  This  process 
is  represented  in  the  equations  by  the  reverse  arrows. 

Catalysis.  —  Catalysis  is  the  process  by  means  of  which  the 
time  reaction  of  chemical  changes  can  be  varied  by  substances 
known  as  catalyzers.  Manganese  dioxide  is  a  classical  example 
of  a  catalyzer.  For  example,  to  make  potassium  chlorate  yield 
up  its  oxygen  it  is  necessary  to  raise  its  temperature  to  about  360 
degrees.  If,  however,  a  little  manganese  dioxide  is  added,  the 
oxygen  is  released  at  a  much  lower  temperature,  vice  200  degrees. 
There  are  many  catalyzers  that  control  chemical  reactions  in  the 
body. 

ENERGY 

Energy  is  ordinarily  defined  as  the  power  of  doing  work.  Ex- 
amples of  various  types  of  energy  are :  mechanical  energy,  heat 
energy,  electrical  energy,  and  chemical  energy.  These  can  be 
transformed  from  one  form  to  another.  To  illustrate :  (1)  elec- 
trical energy  can  be  converted  into  energy  of  motion,  as  evi- 
denced in  the  motor ;  (2)  electrical  energy  can  be  converted  into 
heat  energy,  as  in  the  electric  stove ;  (3)  mechanical  energy  of 
motion  can  be  converted  into  electrical  energy,  as  in  the  dynamo ; 
also,  (4)  chemical  energy  can  be  transformed  into  heat  energy, 
as  is  true  in  the  oxidation  of  food  in  our  bodies. 

SOME  PHYSICAL  TERMS 

Specific  gravity.  —  By  specific  gravity  is  meant  the  comparison 
between  the  weight  of  a  substance  and  the  weight  of  an  equal 
volume  of  some  other  substance  taken  as  a  standard.  The  stand- 
ards usually  referred  to  are  air  for  gases,  and  water  for  liquids  and 
solids.  For  instance,  the  specific  gravity  (sp.  gr.)  of  carbon  dioxide 
(air  standard)  is  1.5,  meaning  that  it  is  1.5  times  as  heavy  as  an 
equal  volume  of  air.  Again  the  specific  gravity  of  mercury  (water 
standard)  is  13.6,  meaning  that  mercury  is  13.6  times  as  heavy  as 
an  equal  volume  of  water.  The  specific  gravity  of  solutions,  as  a 
salt  solution,  will  necessarily  vary  with  the  concentration. 

Diffusion.  —  This  term  in  its  ordinary  use  has  to  do  with  the 
tendency  of  two  liquids  or  two  gases  of  different  densities  to  mix 
uniformly.  Diffusion  can  take  place  either  when  the  substances 


10  ANATOMY  AND   PHYSIOLOGY  [CHAP.  I 

are  simply  superimposed,  or  when  they  are  separated  by  a  mem- 
brane. The  following  illustrations  may  help  to  make  this  clear :  — 

1 .  When  the  gases  or  liquids  are  not  separated  by  a  membrane, 
(a)  If  a  bottle  of  hydrogen  is  inverted  over  a  bottle  of  chlorine 

gas,  the  lighter  hydrogen  molecules  will  move  down  among  the 
chlorine  molecules,  while  the  heavier  chlorine  molecules  will  move 
up  to  mix  with  the  hydrogen  molecules,  so  that  the  two  will  even- 
tually be  mixed  uniformly. 

(6)  If  a  layer  of  water  is  placed  carefully  over  a  layer  of  sulphuric 
acid,  in  such  a  way  that  the  two  do  not  mix,  two  distinct  layers 
will  be  formed  with  the  heavier  sulphuric  acid  at  the  bottom. 
The  acid  molecules  will  begin  to  move  up  and  mix  with  the  water 
molecules,  while  the  water  molecules  will  move  down  to  mix  with 
the  sulphuric  acid  molecules.  The  action  is  much  slower  than  with 
the  gases. 

2.  When  the  gases  or  liquids  are  separated  by  certain  membranes. 

(c)  In  the  illustration  given  in  (a)  if  a  membrane,  permeable 
to  gases/  be  stretched  over  the  mouth  of  the  bottle,  the  gases 
will  mix  evenly  through  it.     Also,  if  a  membranous  sac  of  carbon 
dioxide  is  placed  in  a  vessel  containing  oxygen,  the  two  gases  will 
diffuse  through  the  membrane,  until  the  mixture  of  gases  inside 
and  outside  is  uniform. 

(d)  When  a  bladder  of  alcohol  is  immersed  in  water,  the  two 
liquids  will  diffuse  through  the  membrane;    the  water  diffusing 
more  rapidly  than  the  alcohol,  the  bladder  will  become  distended. 

This  subject  of  diffusion  is  an  important  one  as  the  activities 
which  make  life  possible  for  each  cell  are  dependent  upon  it. 
(See  Respiration,  Circulation,  Metabolism,  and  Excretion.  Pages 
258,  184,  334,  362.) 

The  explanation  of  the  process  is  found  in  the  suppositions  of 
the  kinetic  theory  that :  — 

1.  There  are  spaces  between  the  molecules  making  up  all  fluid 
bodies. 

2.  Molecules  are  in  rapid  motion  in  straight  lines,  the  motion 
of  molecules  of  gases  being  much  more  rapid  and  unrestrained  than 
in  the  case  of  molecules  of  liquids. 

For  an  understanding  of  the  two  forms  of  diffusion  through 
membranes  called  osmosis  and  dialysis,  a  few  definitions  are 
necessary. 


CHAP.  I]     EXPLANATIONS  AND  DEFINITIONS  11 

1.  Permeable  membranes.  —  Permeable  membranes  allow  the 
passage  not  only  of  water  molecules  but  of  substances  in  solution, 
i.e.,  salt  molecules.     If  a  tumbler  be  completely  divided  vertically 
by  a  permeable  membrane,  and  two  ounces  of  salt  solution  placed 
on  one  side  and  four  ounces  of  water  placed  on  the  other,  it  will 
be  found  that  the  water  first  passes  over  to  the  side  containing 
salt  solution ;  later  the  salt  molecules  will  pass  over  to  the  water, 
so  that  eventually  the  quantity  of  water  and  salt  will  be  equal  on 
both  sides  of  the  membrane.     In  other  words  there  will  be  three 
ounces  of  salt  solution  on  each  side  of  the  membrane  instead  of 
two  ounces  of  salt  solution  on  one  side  and  four  ounces  of  water  on 
the  other,  which  was  the  condition  we  started  with. 

2.  Semipermeable  membranes. — Semipermeable   membranes 
allow  the  passage  of  water  molecules  but  not  substances  in  solu- 
tion.    If  our  glass  had  been  divided  by  a  Semipermeable  mem- 
brane, the  water  molecules  could  have  passed  through,  but  not  the 
salt.     Most  of  the  membranes  we  have  in  the  body  are  approxi- 
mately Semipermeable,  i.e.,  they  allow  water  molecules  to  pass 
through   readily,  and  molecules  of  substances  in  solution  less 
readily.     In  such  cases  the  stream  of  water  is  to  the  side  of  the 
dissolved  substance,  but  at  the  same  time  the  molecules  of  this 
substance  pass  to  some  extent  to  the  other  side. 

3.  Osmotic   pressure.  —  In    the    experiment    just    described 
(under  Permeable  Membranes)  it  was  said  that  the  water  passed 
over  to  the  side  of  the  glass  containing  salt  solution.     The  old 
expression   was   that   the  salt  attracted  the  water,  but  in  the 
newer  theories  the  same  fact  is  expressed  by  saying  that  the  salt 
in  solution  exerts  a  certain  osmotic  pressure,  in  consequence  of 
which  more  water  'flows  from  the  water  side  to  the  side  of  the 
salt  solution  than  in  the  reverse  direction.     As  a  matter  of  experi- 
ment it  is  found  that  the  osmotic  pressure  varies  with  the  amount 
of  the  substance  in  solution,  or  in  other  words,  depends  upon  the 
concentration  of  the  solution. 

4.  Isotonic,   Hypertonic,   and   Hypotonic.  —  These   terms  are 
used  to  express  degrees  of  osmotic  pressure  or  differences  in  con- 
centration.    For  instance,  normal  salt  solution  is  used  to  replace 
blood  lost  by  hemorrhage,  because  the  osmotic  pressure  of  normal 
salt  solution  is  equal  to  that  of  blood,  hence  it  is  isotonic  or  isomotic 
to  the  blood,  i.e.,  contains  the  same  amount  of  salt  as  the  blood. 


12  ANATOMY  AND  PHYSIOLOGY  [CHAP.  I 

If  the  solution  contained  a  higher  percentage  of  salt  than  the  blood, 
it  would  be  hypertonic,  if  lower  hypotonic. 

5.  Solution.  —  When  a  substance  disappears  in  a  liquid  in  such 
a  way  as  to  thoroughly  mix  with  it  and  be  lost  to  sight  as  an 
individual  body,  the  resulting  liquid  is  called  a  solution.     It  there- 
fore requires  two  substances  to  make  a  solution,  one  the  liquid  or 
solvent,  and  the  other  the  substance  dissolved  or  solute. 

6.  Osmosis.  —  Osmosis  is  the  passage   of  solvent  molecules 
through  a  membrane. 

7.  Dialysis.  —  Dialysis    is    the    passage    of    solute    molecules 
through  a  membrane. 

8.  Emulsion.  —  An  emulsion  is  a  mixture  of  two  immiscible 
fluids,  where  one  is  scattered  through  the  other  in  the  form  of 
finely  divided  globules. 

UNIT  FOR  MEASURING  HEAT 

Inasmuch  as  heat  is  a  form  of  energy,  it  is  not  as  simple  an  un- 
dertaking to  speak  of  it  in  comparative  terms  as  in  the  case  of 
matter.  It  is  easy  for  one  to  visualize  five  quarts  of  milk  as  five 
times  a  certain  volume  that  has  been  taken  as  a  standard  and  called 
one  quart.  So  it  is  also  with  weights  and  distances,  and  the  meas- 
urement of  weights,  distances,  and  volumes  is  a  necessary  part 
of  our  experience.  It  is  quite  as  urgent  that  there  should  be  a 
basis  for  the  comparison  of  energy  values  as  well  as  for  matter 
values,  else  the  coal  dealer  could  not  place  the  value  of  his  coal  on 
a  basis  of  its  heat-producing  qualities,  nor  could  the  dietitian  plan 
meals  on  a  basis  of  the  ultimate  energy-producing  qualities  to  the 
individual.  We  are  only  conscious  of  energy  as  a  result  of  the  ef- 
fect it  produces,  consequently,  if  it  is  to  be  measured,  it  must  be 
on  this  basis.  In  physiology  the  unit  used  for  measuring  heat  is 
the  calorie. 

Calorie.  —  The  calorie  (Cal.)  is  the  amount  of  heat  that  is  neces- 
sary to  raise  1000  grams  of  water  through  1°  C.  Occasionally  a 
small  calorie  is  used.  This  small  calorie  is  the  amount  of  heat  that 
is  necessary  to  raise  one  gram  of  water  through  1°  C.  It  is,  there- 
fore, only  jinny  a$  large  as  the  calorie. 


CHAPTER  II 

DEFINITIONS.  —  CAVITIES   OF   THE   HUMAN  BODY 
DEFINITIONS 

BEFORE  taking  up  the  study  of  anatomy  and  physiology  in  de- 
tail, it  is  well  to  consider  the  definitions  of  these  terms  as  follows :  — 

Anatomy  refers  to  the  structure  of  an  organism. 

Physiology  refers  to  the  functions  of  an  organism. 

Anatomy  teaches  us  what  organs  a  plant  or  animal  has,  and 
how  they  are  arranged  with  reference  to  one  another.  Physiology 
teaches  us  the  uses  to  which  these  organs  are  put.  Anatomy 
shows  what  an  organ  is ;  physiology  shows  what  an  organ  does. 
Anatomy  may  be,  and  usually  is,  studied  upon  the  dead  creature ; 
physiology  can  be  studied  only  upon  the  living  creature. 

The  anatomical  position.  —  In  describing  the  body,  anatomists 
always  consider  it  as  being  in  the  erect  position,  with  the  face 
toward  the  observer,  the  arms  hanging  at  the  sides,  and  the  palms 
of  the  hands  turned  forward. 

Surfaces  of  the  body.  —  When  the  body  is  in  the  anatomical 
position,  the  front,  or  surface  facing  the  observer,  is  named  the 
ventral  surface.  (See  Fig.  1.)  The  back,  or  surface  directed  away 
from  the  observer,  is  named  the  dorsal  surface.  (See  Fig.  2.) 

The  median  line.  —  This  refers  to  an  imaginary  line  drawn 
through  the  middle  of  the  body,  from  the  top  of  the  head  to  the 
middle  of  the  floor  between  the  feet.  The  parts  nearest  this  line 
are  described  as  medial,  the  parts  farthest  from  this  line  are  de- 
scribed as  lateral. 

Internal  and  external.  —  These  terms  are  used  to  designate 
within  and  without  the  body  itself,  also  within  and  without  the 
body  cavities. 

Proximal  and  distal.  —  Proximal  is  used  to  describe  a  position 
near  the  head  or  source  of  any  part.  Distal  is  used  to  describe  a 

13 


rtrrH  wait  on  irrrtE  TOE 

FOURTH  DIGIT  OK  fOO 

THIRD  DIGIT  OR  THIRD     ._ 

WCOND  DIGIT  OR  MCOND  T 

FIRST  DIGIT  OR  GREAT 


DIOITUS 

DIG1TUS  OUARTQft 
DIGITU8  Tf  RTIUS 
TUSSECUNOU* 
PRIMUS,  HAUUX.  POltrx  H0t» 


FIG.  1.  —  FRONT  VIEW  OF  A  MAN  IN  THE  ANATOMICAL  POSITION.  On  the  right 
lateral  half  the  parts  are  labelled  in  English,  on  the  left  in  Latin.  The  right  upper 
limb  is  drawn  away  from  the  trunk  in  order  to  show  the  arm  more  fully  than  is 
possible  when  it  hangs  perpendicularly.  (Gerrish.) 

14 


MALLEOLU8  EXTERNU9 


FIG    2  -  BACK  VIEW  OF  A  MAN.     On  the  left  lateral  half  the  names  of  the  part* 

are  given  in  English,  on  the  right  in  Latin.     (Gerrisn.) 

15 


16 


ANATOMY  AND   PHYSIOLOGY         [CHAP.  II 


position  distant,  or  farthest  away  from  the  head  or  source  of  any 
part. 

Periphery.  —  This  term  is  used  to  describe  the  circumference 
of  a  circle,  hence  in  anatomy  it  means  the  outside  or  surface  of  a 
body  or  an  organ. 

THE  HUMAN  BODY 

It  is  necessary  to  have  the  clearest  possible  conception  of  the 
main  divisions  and  the  positions  of  the  different  parts  of  the  body, 


NASAL  CAVITY 
BUCCAL  CAVITY 


CRANIAL  ENLARGEMENT 
OF  THE  DORSAL  CAVITY 


DORSAL  CAVITY 
(SPINAL  PORTION) 


BODIES  OF 
VERTE6R/E 


THORACIC  CAVITY 
DJAPHRAGM 

ALIMENTARY  CANAL 
ABDOMINAL  CAVITY 

PELVIC   CAVITY 


FIG.  3.  —  DIAGRAMMATIC  LONGITUDINAL  SECTION  OF  THE  TRUNK  ANF>  HEAD. 
The  alimentary  canal  is  represented  running  through  the  whole  length  of  the 
ventral  cavity. 

and  we  shall  therefore  outline  the  structure  of  the  body  as  a  whole. 
It  is  readily  seen  that  the  human  body  is  separable  into  trunk, 
head,  and  limbs ;  the  trunk  and  head  are  cavities,1  and  contain 

1  In  this  connection  it  is  important  to  emphasize  that  so-called  body  cavities 
are  only  potential  cavities  which  do  not  become  real  ones  unless  their  contents  are 


CHAP.  II] 


CAVITIES 


17 


the  internal  organs  or  viscera,1  while  the  limbs  are  solid,  contain 
no  viscera,  and  are  merely  appendages  of  the  trunk. 

Cavities  of  the  body.  —  The  trunk  and  head  contain  two  main 
cavities,  and  looking  at  the  body  from  the  outside  we  should 
naturally  imagine  that 
these  two  cavities  were 
the  cavity  of  the  head 
and  the  cavity  of  the 
trunk,  respectively.  If, 
however,  we  divide  the 
trunk  and  head  length- 
wise into  two  halves,  by 
cutting  them  through 
the  middle  line  from 
before  backwards,  we 
find  the  trunk  and  head 
are  divided  by  the 
bones  of  the  spine  into 
dorsal  and  ventral  cav- 
ities, and  not  into 
upper  and  lower.  (See 
Fig.  3.) 

1.  Dorsal  cavity.  - 
The     dorsal    or    back 
cavity    is    a    complete 
bony    cavity,    and    is 
formed  by   the   bones 
of  the  skull,   and  the 
vertebrae  (bones  of  the 
spine) .    It  may  be  sub- 
divided into :  — 

a.  The  cranial  cavity.  —  This  cavity  contains  the  brain. 

b.  The  spinal  canal.  —  This  canal  contains  the  spinal  cord, 
which  is  continuous  with  the  brain. 

2.  Ventral  cavities.  —  The  ventral  or  front  cavities  are  not  corn- 
removed.     In  life  they  are  completely  filled  by  the  organs  plus  a  small  quantity 
of  fluid. 

1  Viscera  is  the  plural  of  the  Latin  word  viscus,  which  means  an  organ  ;    hence 
viscera  are  organs  contained  within  the  body  cavities.     Example  :   heart,  stomach, 
etc.     Each  of  these  may  be  called  a  viscus, 
C 


FIG.  4.  —  POSITION    OF    THE  THORACIC    AND   AB- 
DOMINAL ORGANS  (FRONT  VIEW).    (Morrow.) 


18 


ANATOMY  AND  PHYSIOLOGY         [CHAP.  II 


plete  bony  cavities,  part  of  their  walls  being  formed  of  muscular 
and  other  tissue. 

a.  Orbital  cavity.  —  The  orbital  cavity  contains  the  eye,  the 
optic  nerve,  the  muscles  of  the  eyeball,  and  the  lacrimal  apparatus. 

b.  Nasal    cavity.  — 
The   nasal    cavity    is 
filled  in  with  the  struc- 
tures forming  the  nose. 

c.  Buccal   cavity.  — 
The  buccal  cavity  or 
mouth     contains     the 
tongue,      teeth,      and 
salivary  glands. 

d.  Thoracic     cavity. 
-  The  thoracic  cavity, 

or  chest,  contains  the 
trachea  or  windpipe, 
the  lungs,  oesophagus 
or  gullet,  heart,  and  the 
great  vessels  springing 
from,  and  entering 
into,  the  heart. 

Diaphragm.  -  -  The 
diaphragm  is  a  dome- 
shaped  membranous 
and  muscular  partition 
between  the  thoracic 
and  abdominal  cavi- 
ties. 

e.  Abdominal  cavity. 
-The     abdominal 

cavity     contains     the 

stomach,  liver,   gall-bladder,  pancreas,   spleen,   small   and  large 
intestines. 

/.  Pelvic  cavity.  —  The  pelvic  cavity  is  that  portion  of  the  ab- 
domen lying  below  an  imaginary  line  drawn  across  the  prominent 
crests  of  the  hip  bones.  It  is  more  completely  bounded  by  bony 
walls  than  the  rest  of  the  abdominal  cavity.  It  is  divided  by  a 
narrowed  bony  ring  into  the  large  (false),  and  small  (true)  pelvis. 


FIG.  5.  —  POSITION   OF   THE   THORACIC   AND  AB- 
DOMINAL ORGANS  (REAR  VIEW).    (Morrow.) 


CHAP.  II] 


SUMMARY 


19 


(See  Fig.  59.)     The  small  or  true  pelvis  contains  the  bladder, 
rectum,  and  some  of  the  generative  organs. 

The  limbs,  or  extremities,  upper  and  lower,  are  in  pairs,  and 
bear  a  rough  resemblance  to  one  another,  the  shape  of  the  bones, 
and  the  disposition  of  the  muscles  in  the  thigh  and  arm,  leg  and 
forearm,  ankle  and  wrist,  foot  and  hand,  being  very  similar. 
There  is,  however,  a  marked  difference  between  the  mobility  of 
the  upper  and  the  lower  limbs.  The  shoulder  is  freely  movable, 
not  so  the  hip. 


HUMAN 
BODY 


Dorsal  Cavity 


Ventral  Cavities 


a.  Orbital  cavity 


b.  Nasal  cavity 


d.  Thoracic 
cavity 


SUMMARY 

a.  Cranial  cavity  —  Brain. 

b.  Spinal  canal  —  Spinal  cord. 

Eye. 

Optic  nerve. 

Muscles  of  the  eyeball. 

Lacrimal  apparatus, 
f  Structures  forming  the 
1      nose. 
f  Tongue. 

c.  Buccal  cavity    <  Teeth. 

I  Salivary  glands. 

f  (Esophagus  —  Trachea. 

{  Lungs  —  Heart. 

I  Blood-vessels. 

the   thoracic 


Abdominal 
cavity 


The    Diaphragm    separates 
and  abdominal  cavities. 

Stomach  —  Spleen  — 

Pancreas. 

Liver  —  Gall-bladder. 
Large    and    small    in- 
testines -  -  Kidneys 
(behind     the     peri- 
toneum) . 

1.  Large  (false)  pelvis. 

2.  Small  (true)  pelvis. 
Bladder  —  Rectum. 
Some  of  the  genera- 
tive organs. 


/.    Pelvic  cavity 


CHAPTER  III 

CELLS,  TISSUES,  ORGANS,  AND  SYSTEMS.  —  EPITHELIAL  TISSUE 

-NERVE   TISSUE 

FROM  the  standpoint  of  the  chemist  the  body  is  composed  of 
elements.  (See  page  3.)  From  the  standpoint  of  the  anatomist 
the  body  is  composed  of  cells,  and  they  are  regarded  as  the  struc- 
tural units  out  of  which  either  directly  or  indirectly  it  is  built. 
If  the  substance  of  any  part  of  the  body,  i.e.,  skin,  muscle,  or 
blood,  is  examined  with  the  unaided  eye,  it  appears  homogeneous, 
but  if  examined  with  the  microscope  it  is  found  to  be  composed  of 
an  innumerable  number  of  minute  cells.  It  is  helpful  to  recall 
that  low  down  in  the  scale  of  life  we  find  animals  so  simple  that 
they  are  described  as  consisting  of  just  one  cell.  These  unicellular 
animals  are  alive  because  they  are  capable  of  carrying  on  the 
biological  functions  which  are  essential  to  life.  As  we  ascend  in 
the  scale  of  life,  we  find  animals  that  consist  of  a  greater  number 
of  cells.  The  human  animal  may  be  properly  described  as  a 
multicellular  animal  consisting  of  an  enormous  aggregate  of  cells. 
It  is  important  to  remember  that  each  individual  cell  that  enters 
into  the  structure  of  a  multicellular  animal  is  capable  of  carrying 
on  the  biological  functions  just  as  the  one  cell  that  forms  the  uni- 
cellular animal. 

Hence,  all  the  varied  activities  of  the  body  are  the  result  of  the 
activities  of  the  cells  which  compose  it,  and  it  is  very  desirable 
that  we  early  acquire  some  definite  conception  of  these  tiny  ele- 
mentary bodies. 

CELLS 

A  cell 1  is  a  minute  portion  of  living  substance  called  proto- 
plasm which  is  sometimes  enclosed  in  a  cell- wall.  Within  the  pro- 

1  The  word  cell  is  from  the  Latin  cella  —  a  cavity  —  and  was  first  used  by  bot- 
anists to  describe  plant  cells,  like  those  of  cork  and  elder  pith,  which  have  cavities 
in  their  substance.  It  is  now  known  that  most  animal  cells,  and  many  plant  cells, 
do  not  have  cavities,  so  that  the  name  is  not  especially  appropriate,  but  it  is  too 
firmly  fixed  in  our  language  to  be  abandoned. 

20 


CHAP.  Ill] 


CELLS 


21 


Protoplasm  (living) 


toplasm  lies  a  body  of  definite  rounded  form,  called  the  nucleus, 
and  this  in  turn  often  contains  one  or  more  smaller  bodies  or 
nucleoli. 

Cytoplasm. 

f  Chromatin. 
Nucleus  <  .   , 

I  Achromatm. 

Cell     {  Centrosome. 

[  Food. 
Metaplasm  (not  living)  |  Wastes. 

[  Storage  Products. 

Protoplasm.  —  Protoplasm  is  a  general  term  for  living  substance. 

Cytoplasm.  —  That  portion  of  the  protoplasm  which  surrounds 
the  nucleus  is  given  the  name  cytoplasm.  Cytoplasm  is  therefore 
a  regional  name  for  a  portion  of  the  protoplasm. 

ATTRACTION-SPHERE   ENCLOSING 
TWO    CENTROSOMES 


NUCLEOLUS 
NUCLEUS 


VACUOLE 


PASSIVE   BODIES 

(METAPLASM  SUSPENDED 
IN  THE  CYTOPLASMIC 
MESHWORK) 


FIG.  6.  —  DIAGRAM  OF  A  CELL.     (Modified  from  Wilson.) 

Nucleus.  —  That  portion  of  the  protoplasm  inside  the  nuclear 
membrane  is  called  the  nucleus.  It  is  more  solid,  differs  in  chemi- 
cal composition,  and  may  or  may  not  contain  the  minute  spherical 
bodies  termed  nucleoli.  In  red  blood  cells  no  nucleus  can  be  found. 
It  is  known,  however,  that  when  first  formed  each  has  a  nucleus 
though  it  is  lost  in  the  course  of  development.  If  an  attempt 


22  ANATOMY  AND  PHYSIOLOGY        [CHAP.  Ill 

is  made  to  dye  the  nucleus  with  chromatin  dyes,  certain  portions 
will  take  the  dye,  other  portions  will  not.  The  material  which 
can  be  dyed  is  called  chromatin,  the  matter  which  cannot  be  dyed 
is  called  achromatin. 

Centrosome.  —  An  actively  multiplying  cell  contains  a  minute 
structure  called  the  centrosome  which  is  associated  with  the 
reproductive  function.  It  is  found  in  or  near  the  nucleus,  and  is 
usually  surrounded  by  a  mass  of  slightly  differentiated  cytoplasm 
called  the  attraction  sphere. 

Metaplasm.  —  In  the  mesh  work  of  protoplasm  are  often  sus- 
pended various  passive  bodies,  such  as  food  granules,  pigment 
bodies,  drops  of  oil,  etc.  These  may  represent  reserve  food  mat- 
ters, or  waste  matters,  and  are  collectively  designated  as  meta- 
plasm,  or  non-living  substances. 

Life  activities  in  cells.  —  Since  the  body  is  composed  of  cells, 
it  follows  that  all  the  activities  of  the  body  are  the  result  of  the 
activities  of  the  cells.  These  activities  are  designated  as  the 
biological  functions  which  are  essential  to  life.  They  may  be 
enumerated  as  follows  :  — 

(1)  Support.  —  Each  cell  is  afforded  support  by  the  cohesiveness 
of  its  own  structure;   by  the  cell-wall  if  one  exists;    if  not,  then 
the   outer   circumference    of   the   protoplasm    approximates   the 
function  of  a  membranous  support. 

(2)  Respiration.  —  Each  cell  coming  in  contact  with  oxygen 
absorbs  it.     Whenever  this  absorption  takes  place  a  certain  amount 
of  the  cell-contents  is  burned  or  oxidized,  and  as  a  result  of  this 
oxidation  heat  and  other  kinds  of  energy  are  produced,  and  car- 
bon dioxide,  which  is  a  waste  product,  is  formed.     Thus  it  will  be 
seen  that  the  real  purpose  of  respiration  is  to  furnish  oxygen  to 
each  individual  cell,  and  to  take  from  the  cell  the  carbon  dioxide 
which  it  does  not  need. 

(3)  Metabolism.  —  Each  cell  is  able  to  take  to  itself,  and  even- 
tually convert  into  its  own  substance,  certain  materials  (foods) 
that  are  non-living ;   in  this  way  the  protoplasm  may  increase  in 
amount,  or,  in  other  words,  the  cell  may  grow.     The  amount  of 
protoplasm  is  not  permanently  increased,  because  only  enough 
protoplasm  is  added  by  the  process  of  assimilation  to  replace  that 
incidentally    oxidized.     Chemical    changes    which    involve    the 
building  up  of  living  material  within  the  cell  have  received  the 


CHAP.  Ill] 


CELLS 


23 


general  name  of  anabolic  changes,  or  andbolism;  on  the  other 
hand,  those  which  involve  the  breaking  down  of  such  material 
into  other  and  simpler  products  are  known  as  katabolic  changes,  or 
katabolism,  while  the  sum  of  all  the  anabolic  and  katabolic  changes 
which  are  proceeding  within  the  cell  is  spoken  of  as  the  metabolism 
of  the  cell.  These  chemical  changes  are  always  more  marked  as 


FOOD 


ANABOLISM 


ENERGY 
(GIVEN  OFF  BY 

CARBOHYDRATES 

FATS 

EXCESS  PROTEINS) 


EXCRETIONS 

CARBON  DIOXIDE 
WATER 

NITROGEN 


OXYGEN 


KATABOLISM 
FIG.  7.  —  DIAGRAM  SHOWING  PROCESS  OF  METABOLISM  IN  A  CELL. 

the  activity    of   the    cell   is  promoted  by  warmth,  electrical  or 
other  stimulation,  the  action  of  certain  drugs,  etc. 

(4)  Motion.  —  This  is  exhibited  in  two  different  forms  :  - 

(a)  Amoeboid    movement.  —  This    term   is   derived    from    the 
amoeba,  a  single-celled  organism.     It  consists  in  the  pushing  out- 
ward by  the  cell  of  processes,  called  pseudopodia.     These  may  be 
retracted  or  the  contents  of  the  cell  may  flow  into  them.     In  this 
way  the  cell  may  change  both  its  shape  and  position.     By  a  repe- 
tition of  this  process  the  cell  may  move  slowly  away  from  its  original 
situation,  so  that  an  actual  locomotion  takes  place. 

(b)  Ciliary   movement. --This    is    the   whipping   motion   pos- 
sessed by  little  hair-like  processes  called  cilia,  which  project  from 
the  surface  of  some  epithelial  cells. 

(5)  Circulation.  —  This  consists  in  a  "  streaming  "  of  the  proto- 
plasm, which  occurs  within  the  limits  of  the  cell.     By  this  means 
nutritive  material  or  waste  substances  may  be  carried  from  one 
portion  of  the  cell  to  another. 


24 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  Ill 


FIG.  8.  —  DIAGRAMS  TO  SHOW  THE  SEQUENCE 
OF  EVENTS  IN  MITOSIS.  A,  resting  cell  with 
nucleus  (ri)  and  centrosome  (c).  B,  preparing 
to  divide,  two  asters  (a)  near  nucleus,  each  with 
a  centrosome,  chromatin  being  massed  into 
chromosomes.  C,  centrosomes  separating  form- 
ing a  spindle  between  them,  nuclear  membrane 
disappearing,  chromosomes  formed.  D,  chro- 
mosomes (ch)  lying.in  the  equator  of  the  spindle. 

E,  chromosomes  divided  lengthwise  into  halves. 

F,  chromosomes  separating  and  moving  toward 
the  centrosomes.     G,  chromosomes  forming  the 
two  nuclei,  arid  cell  body,  beginning  to  divide. 
H,  division  complete,  two-cell  stage ;  each  cell 
has  the  same  structure  as  the  one-cell   in  A. 
(Modified  from  Wilson.) 


(0)  Excretion.  -  Kndi 
cell  is  able  to  discharge 
and  thus  get  rid  of  waste 
substances. 

(7)  Irritability.  -  -  Ir- 
ritability is  that  property 
which     enables     a    cell 
to  respond    to    external 
stimuli.      Cells   vary   in 
regard    to    their    irrita- 
bility, the  most  markedly 
irritable    cells   in  higher 
animals    being  those  of 
the  nervous  system. 

(8)  Cell      division.  - 
Like  all  living  organisms, 
each  cell  grows,  produces 
other  cells,  and  dies,  so 
that  each  cell  has  a  life 
cycle  comparable  to,  but 
much  shorter  than,  the 
body  itself.     As  the  cells 
are  constantly  dying,  the 
need  for  constant  repro- 
duction is  apparent.  This 
reproduction    is    accom- 
plished    in    two    ways, 
(a)  simple  direct  division 
and  (b)  indirect  division 
or  mitosis  which  is  the 
almost  universal  method. 

(a)  In  direct  division 
the  cell  elongates,  the 
nucleus  and  cytoplasm 
become  constricted  in 
the  centre,  and  the  cell 
divides  and  forms  two 
cells  which  soon  grow  to 
the  size  of  the  original  cell. 


CHAP.  Ill]  CELLS          .  25 

(6)  In  indirect  division,  or  mitosis,  the  nucleus  passes  through 
a  series  of  remarkable  changes  which  are  rather  complicated.  A 
careful  study  of  Fig.  8  will  give  the  student  some  idea  of  these 
changes.1 

Differences  in  cells.  —  Cells  differ  in  (1)   size,  (2)  form,  (3) 
chemical  composition,  and  (4)  function.       (1)  As  an  example  of 
variation  in  size  2  a  voluntary  muscle  cell  is  about  an  inch  (25  mm.) 
long  and  3-^  of  an 
inch  (0.05  mm.)  in 
diameter.     The      o 
processes  of  a  nerve  C~~  ^  A 

Cell  may  be  3  feet  FIG.  9.  —  SIZES  OF  CELLS.     A,  voluntary  muscle  cell 

a\  magnified  in  width  200  times  and  represented  as  cut 

metrej    Or    more  off  at  <?      At  this  magnification  it  would  be  about  200 

ill    length        A    red  inches  long.     B,  red  blood  cell,  also  magnified  about 

•  200  times. 

blood    cell    has    a 

diameter  of  3-^^  of  an  inch  (about  0.008  mm.).  (2)  The  simplest 
form  of  cell  is  spherical,  but  this  is  seldom  realized  except  in 
unicellular  plants  and  animals.  In  the  human  body  the  form 
of  the  cell  is  modified  by  the  pressure  of  the  surrounding  struc- 
tures, by  active  movement  of  the  cell  substance,  and  by  growth 
and  differentiation.  (3)  It  is  assumed  that  the  marked  difference 
in  the  appearance  of  cells  is  an  expression  of  a  chemical  differ- 
ence, which  in  turn  is  an  evidence  of  difference  in  function. 
(4)  A  unicellular  animal  is  in  itself  a  complete  living  thing,  and 
thus  one  cell  must  perform  all  the  essential  activities  of  life, 
and  is  self-sufficient.  In  multicellular  animals  there  is  a  physio- 
logical division  of  labor  among  the  cells,  i.e.,  certain  cells  have 
become  specialized  in  some  one  essential  activity  which  they 
perform  for  the  whole  complex,  and  certain  others  have  become 
specialized  to  perform  other  essential  activities  for  the  whole, 

1  For  a  detailed  description  of  mitosis  the  student  is  referred  to  "The  Cell  in 
Development  and  Inheritance,"  by  Wilson. 

2  On  page  491  will  be  found  accurate  ratios  between  the  metric  system  and  the 
system  of  lengths,  weights,  and  measures  used  in  the  United  States.     For  the  sake 
of  simplicity  in  converting  figures  in  the   text  from  one  system  to  the  other,  we 
have  assumed 

1  cm.  to  equal  g  in.  (25  mm.   =  1  in.). 

1  cc.  to  equal  15  minims. 

30  gm.  to  equal  1  oz.  (dry  or  liquid  measure). 

30  cc.  to  equal  1  oz.  (dry  or  liquid  measure). 

1  litre  to  equal  1.75  pt.  (dry  measure). 

1  litre  to  equal  2.11  pt.  (liquid  measure). 


26  ANATOMY  AND   PHYSIOLOGY        [CHAP.  Ill 

i.e.,  the  function  of  muscle  cells  is  to  contract,  and  the  combined 
contraction  of  a  group  of  muscle  cells  results  in  the  contraction  of 
a  muscle. 

TISSUES 

The  cells  of  the  body  are  arranged  in  groups  called  tissues. 
Each  tissue  is  a  collection  of  cells  of  like  substance  arranged  to- 
gether and  having  some  specialized  function  to  perform  for  the 
body.  In  many  tissues,  all  the  substance  is  not  inside  the  cell- 
walls,  some  of  it  is  between  the  cells  or  intercellular.  In  the 
muscles  there  is  a  cement  substance  between  the  cells  which  holds 
them  together.  In  some  tissues  there  is  very  little  intercellular 
substance,  in  others  there  is  a  large  proportion  of  it. 

ORGANS 

When  two  or  more  different  tissues  are  associated  in  performing 
some  special  office  in  the  body,  the  part  so  adapted  is  termed  an 
organ.  Thus,  the  bones  are  organs  specially  adapted  for  support 
and  locomotion,  the  kidneys  for  secreting  urine,  etc.  As  the  struc- 
ture of  an  organ  depends  upon  the  properties  of  the  tissues  com- 
posing it,  so  the  characteristics  of  each  tissue  depend  upon  their 
ultimate  structural  units  —  the  cells  and  the  intercellular  sub- 
stance. 

SYSTEMS 

An  arrangement  of  organs  closely  allied  to  each  other  and  set 
apart  to  perform  some  general  function  is  spoken  of  as  a  system. 
Eight  systems  are  found  in  the  human  body.  Their  names  with 
the  functions  of  each  are  briefly  expressed  as  follows :  — 

Skeletal  system.  —  Support. 

Respiratory  system.  —  To  provide  oxygen  and  get  rid  of  carbon 
dioxide. 

Alimentary  system. —  To  receive,  digest,  and  absorb  the  food 
which  is  to  be  used  by  the  cells. 

Muscular  system.  —  Contraction  which  results  in  motion. 

Vascular  system.  —  Distribution  of  the  body  fluids  to  all  the 
cells. 

Excretory  system.  —  To  eliminate  the  waste  products  that 
result  from  cell  activity. 


CHAP.  Ill]  CLASSIFICATION  27 

Nervous  system.  —  To  control  and  insure  coordination  in  the 
working  of  all  the  systems  in  the  body.  Contains  the  centres  for 
all  the  sensations,  intelligence,  and  thought  that  we  recognize  as 
the  highest  functions  of  life. 

Reproductive  system.  —  To  insure  the  continuance  of  the  race 
by  the  production  of  other  beings. 

It  is  important  for  the  student  to  remember  that  these  different 
systems  are  closely  interrelated  and  dependent  on  each  other. 
While  each  forms  a  complete  unit,  specially  adapted  for  the  per- 
formance of  some  function,  yet  that  function  cannot  be  properly 
performed  without  the  assistance  and  cooperation  of  other  systems. 
The  most  perfect  skeleton  is  not  capable  of  support  unless  assisted 
by  the  muscular  and  nervous  systems.  Any  interference  with  the 
circulatory  system  also  affects  the  work  of  the  excretory  system, 
etc. 

CLASSIFICATION 

By  the  aid  of  the  microscope  the  different  distinct  tissues  of 
which  the  body  is  formed  are  found  to  be  comparatively  few  in 
number,  and  some  of  these,  although  at  first  sight  apparently  dis- 
tinct, yet  have  so  much  in  common  in  their  structure  and  origin, 
one  with  another,  that  the  number  becomes  still  further  reduced, 
until  we  can  distinguish  only  four  distinct  tissues,  viz. :  - 

1.  The  epithelial  tissues.        3.   The  connective  tissues. 

2.  The  nerve  tissues.  4.   The  muscular  tissues. 

Such  fluids  as  blood  and  lymph  are  frequently  described  as  liquid 
tissues. 

Origin  of  tissues.  —  It  has  been  stated  that  the  cell  is  the 
structural  unit  of  the  body,  and  in  the  beginning  the  body  de- 
velops from  a  single  cell  called  a  zygote  which  is  formed  by  the 
union  of  the  ovum  and  the  spermatozoon.  The  ovum  is  de- 
veloped in  the  ovary  and  is  made  fertile  by  the  entrance  into  it 
of  a  cell,  known  as  the  spermatozoon  formed  in  the  testes  of  the 
male.  After  fertilization  takes  place  the  zygote  divides  and  sub- 
divides until  an  enormous  number  of  cells  is  formed.  The  cells 
thus  formed  arrange  themselves  in  the  form  of  a  membrane, 
blastoderm,  which  is  composed  of  three  layers.  These  layers  are 
known  respectively  as  ectoderm,  mesoderm,  and  entoderm. 


28  ANATOMY  AND   PHYSIOLOGY        [CHAP.  Ill 

The  ectoderm,  or  outer  layer,  forms  the  epidermis  and  the  ner- 
vous system. 


FIG.  10.  —  DIAGRAMS  TO  ILLUSTRATE  FERTILIZATION  OF  AN  EGG-CELL  (OVUM) 
BY  A  SPERM-CELL  (SPERMATOZOON).  A,  e,  nucleus  of  a  matured  egg-cell;  s,  a 
sperm-cell  ready  to  enter.  B,  sperm-cell  entered  and  transformed  into  sperm- 
nucleus  (s).  C,  sperm-nucleus  and  egg-nucleus  united,  fertilization  complete, 
zygote  formed.  D,  division  leading  to  two-cell  stage.  (Bigelow.) 

The  mesoderm,  or  middle  layer,  forms  the  circulatory  and  most 
of  the  genito-urinary  systems,  also  the  muscles,  bones,  and  other 
connective  tissues. 

The  entoderm  or  inner  layer  forms  the  greater  part  of  the  lining 
of  the  alimentary  and  respiratory  tracts,  also  the  liver,  pancreas, 
and  other  glands. 

EPITHELIAL  TISSUE 

Epithelial  tissue  is  composed  entirely  of  cells  united  by 
cement  substance.  The  cells  are  generally  arranged  so  as  to  form 
a  skin,  or  membrane,  covering  the  external  surfaces,  and  lining 
the  internal  parts  of  the  body.  This  membrane  is  seen  when  the 
skin  is  blistered,  the  thin  and  nearly  transparent  membrane  raised 
from  the  surface  being  epithelial  tissue  —  in  this  situation  called 
epidermis,  because  it  lies  upon  the  surface  of  the  true  skin.  In 
other  situations,  epithelial  tissue  usually  receives  the  general  name 
of  epithelium. 

We  may  classify  the  varieties  of  epithelium  according  to  the 
shape  of  the  cells  which  compose  them,  or  according  to  the  ar- 
rangement of  these  cells  in  layers.  Adopting  the  latter  and  simpler 
classification,  we  distinguish  three  main  varieties :  — ' 

1.  The  simple,  consisting  of  a  single  layer  of  cells. 

2.  The  transitional,  consisting  of  two  or  three  layers. 

3.  The  stratified,  consisting  of  many  layers. 

1.  Simple  epithelium.  — This  is  composed  of  a  single  layer  of 
cells.  The  cells  forming  single  layers  are  of  distinctive  shape, 


CHAP.  Ill] 


EPITHELIAL   TISSUE 


29 


FIG.  11.— SIMPLE  PAVE- 
MENT EPITHELIUM.  a, 
from  a  serous  membrane ; 
b,  from  a  blood-vessel. 


and  have  distinctive  functions  in  different  parts  of  the  body.     The 
chief  varieties  are  :  — 

a.  pavement  b.   columnar  c.   ciliated 

(a)  Pavement  epithelium.  —  This   is  also   called   squamous   or 
scaly  epithelium.     The  cells  form  flat,  many-sided  plates  or  scales, 
which    fit    together    like    the    tiles    of    a 

mosaic  pavement.  It  forms  very  smooth 
surfaces,  and  lines  the  heart,  blood- 
vessels, lymphatics,  and  the  serous  cavi- 
ties, etc. 

(b)  Columnar  epithelium.  —  The  colum- 
nar   epithelium    is   a    variety    of    simple 
epithelium    in    which    the    cells   have   a 
prismatic  shape,  and  are  set  upright  on 

the  surface  which  they  cover.  In  profile  these  cells  look  some- 
what like  a  close  palisade.  They  taper 
somewhat  toward  their  attached  end,  which 
is  set  upon  a  basement  membrane.  Colum- 
nar epithelium  is  found  in  its  most  charac- 
teristic form  lining  the  intestinal  canal. 

(c)  Ciliated  epithelium.  —  In  ciliated  epi- 
thelium the  cells,  which  are  generally  co- 
lumnar in  shape,  bear  at  their  free  surface 

little  hair-like  processes,  which  are  agitated  incessantly  with  a 

lashing  or  vibrating  motion.     These  minute  and  delicate  processes 

are    named    cilia,    and    are 

active  prolongations  of  the 

cell-protoplasm.      The  man- 
ner  in  which  cilia  move   is 

best  seen  when  they  are  not 

acting    very   quickly.      The 

motion     of     an     individual 

cilium  may  be  compared  to 

the    lash-like    motion    of    a 

short-handled      whip,      the 

cilium  being  rapidly  bent  in 

one  direction.     The  motion 

does  not  involve  the  whole  of  the  ciliated  surface  at  the  same 

moment,  but  is  performed  by  the  cilia  in  regular  succession,  giv- 


FIG.  12.— SIMPLE  CO- 
LUMNAR EPITHELIUM,  a, 
the  cells  ;  b,  intercellular 
substance  between  the 
lower  end  of  cells. 


FIG.  13.  —  CILIATED  EPITHELIUM  FROM 
THE  HUMAN  TRACHEA.  (Highly  magnified.) 
a,  large  ciliated  cell ;  d,  cell  with  two  nuclei. 


30  ANATOMY  AND  PHYSIOLOGY        [CHAP.  Ill 

ing  rise  to  the  appearance  of  a  series  of  waves  travelling  along 
the  surface  like  the  waves  tossed  by  the  wind  in  a  field  of  wheat. 
When  they  are  in  very  rapid  action,  their  motion  conveys  the 
idea  of  swiftly  running  water.  As  they  all  move  in  one  direc- 
tion, a  current  of  much  power  is  produced. 

In  man  their  use  is  to  impel  secreted  fluids,  or  other  matters, 
along  the  surfaces  from  which  they  extend ;  as,  for  example,  the 
mucus  of  the  trachea  and  nasal  chambers,  which  they  carry  toward 
the  outlet  of  these  passages. 

2.  Transitional  epithelium.  —  This  consists  of  two  or  three 
layers  of  cells.  The  superficial  cells  are  large  and  flattened,  hav- 


FIG.  14.  —  SECTION  OF  THE  TRANSITIONAL  EPITHELIUM  LINING  THE  BLADDER. 
(Highly  magnified.)  a,  superficial ;  6,  intermediate ;  c,  deep  layer  of  cells. 
(Schafer.) 

ing  on  their  under  surface  depressions  into  which  fit  the  larger 
ends  of  the  pear-shaped  cells  which  form  the  next  layer.  Be- 
tween the  tapering  ends  of  these  pear-shaped  cells  are  one  or  two 
layers  of  smaller,  many-sided  cells,  the  epithelium  being  renewed 
by  division  of  these  deeper  cells.  This  kind  of  epithelium  lines 
the  bladder  and  ureters. 

3.  Stratified  epithelium. — This  consists  of  many  layers  of 
cells.  The  cells  composing  the  different  layers  differ  in  shape. 
As  a  rule,  the  cells  of  the  deepest  layer  are  columnar  in  shape; 
the  next,  rounded  or  many-sided,  whilst  those  nearest  the  surface 
are  always  flattened  and  scale-like.  The  deeper  soft  cells  of  a 
stratified  epithelium  are  separated  from  one  another  by  a  system 
of  channels,  which  are  bridged  across  by  numerous  fibres.  These 
cells  are  often  described  as  prickle  cells,  as  when  separated  they 
appear  beset  with  spines.  They  are  continually  multiplying  by 


CHAP.  Ill]  EPITHELIAL  TISSUE  31 

cell-division,  and  as  the  new  cells  which  are  thus  produced  in  the 
deeper  parts  increase  in  size,  they  compress  and  push  outward 
those  previously  formed.  In  this  way  cells  which  were  at  first 
deeply  seated  are  gradually  shifted  outward  and  upward,  growing 
harder  as  they  approach  the  surface.  The  older  superficial  cells 


FIG.  15.  —  SECTION  OF  STRATIFIED  EPITHELIUM,  c,  lowermost  columnar  cells ; 
P,  polygonal  cells  above  these ;  fl,  flattened  cells  near  the  surface.  Between  the 
cells  are  seen  intercellular  channels,  bridged  over  by  processes  which  pass  from  cell 
to  ceil.  (Schafer.) 

are  being  continually  rubbed  off  as  the  new  ones  continually  rise 
up  to  supply  their  places. 

Stratified  epithelium  covers  the  anterior  surface  of  the  eye, 
lines  the  mouth,  the  chief  part  of  the  pharynx,  the  oesophagus,  the 
anal  canal,  part  of  the  urethra,  and  in  the  female  the  vagina  and 
neck  of  the  uterus. 

Its  most  extensive  distribution  is  over  the  surface  of  the  skin, 
where  it  forms  the  epidermis.  Whenever  a  surface  is  exposed  to 
friction,  we  find  stratified  scaly  epithelium,  and  we  may  therefore 
classify  it  as  a  protective  epithelium. 

Function.  —  The  most  important  functions  of  epithelial  tissue 
are  as  follows  :  — 

1.  Protection.  — Some  varieties  are  specially  modified  so  as  to 
form  protective  membranes.     Example  —  skin.     Other  varieties 
form  the  top  layer  of  the  mucous  membranes,  and  mucous  mem- 
branes are  found  lining  passages  that  communicate  with  the  ex- 
terior of  the  body.     Serous  membranes  are  also  lined  by  epithelial 
cells.     These  serous  membranes  line  passages  that  do  not  com- 
municate with  the  exterior  of  the  body. 

2.  Motion.  — This  is  seen  in  the  cilia,  which  tend  to  keep  the 
passages  from  which  they  extend  clean  and  free  from  foreign  ma- 
terial. 


32 


ANATOMY   AND   PHYSIOLOGY        [CHAP.  Ill 


3.  Absorption.  —  This  is  particularly  well  seen  in  the  digestive 
tract. 

4.  Secretion.  —  Every  secreting  organ  must  contain  epithelial 
cells.     Mucous  and  serous  membranes  are  examples  of  secreting 
organs. 

5.  Special  sensation.  —  The  organs  of  the  special  senses   con- 
tain epithelial  cells.     Examples  —  eye,  ear,  nose,  etc. 

NERVE  TISSUE 

Nerve  tissue  like  all  other  tissues  is  composed  of  cells  which 
are  differentiated  from  other  cells  in  that  their  protoplasm  is  ex- 
tended, often  to  a  distance  of  two  or  three  feet,  to  form  thread-like 
processes  or  conductors.  The  cells  and  their  processes  are  held 
in  place  by  a  peculiar  form  of  connective  tissue  called  neuroglia 
or  glia  tissue.  (See  page  50.)  The  cells  of  the  nervous  system 
are  called  neurones. 

NEURONES 

Although  the  neurones  vary  considerably  in  size  and  form, 
they  possess  certain  structural  char-  ( ,  ( 

acteristics    in   common.     They   con-  /        \  I 

.  ±    e  f  c  /      t  ^  <         (/ 

sist  or :  — 

(1)  The  cell-body 

(2)  The  cell-processes 


FIG.  16.  —  DIFFERENT  TYPES  OF  NEURONES.  A,  pyramidal  cell  from  cerebral 
cortex.  B,  bipolar  colls  of  the  Spinal  Sensory  Ganglia.  C,  cell  of  Purkinje  from 
the  Cerebellum.  (Burton-Opitz.) 


CHAP.  Ill] 


NERVE  TISSUE 


33 


These  two  parts  make  up  a  complete  nervous  entity,  and  the  en- 
tire nervous  system  consists  of  an  enormous  number  of  neurones. 

(1)  The  cell-body.  —  The  cell-bodies  vary  as  to  size  and  shape, 
but  all  varieties  present  certain  common  characteristics.     A  typical 
cell-body  consists  of  a  mass  of  granular  cytoplasm  surrounding  a 
large,  well-defined  nucleus.    The  latter  in  turn  contains  a  nucleolus. 
From  the  angles  of  the  cell-body  are  given  off  processes.     Each 
cell-body  has  at  least  one  process  and  may  have  many  more. 

Function  of  the  cell-body.  —  The  cell-body  affords  nutriment  to 
its  processes,  as  is  proven  by  the  fact  that  if  a  nerve-fibre  is  cut,  the 
part  separated  from  the  cell-body  dies.  Moreover,  they  are  ca- 
pable of  modifying  impulses  brought  to  them  by  their  sensory  pro- 
cesses. This  modification  may  take  the  form  of  inhibition  and 
either  partially  or  completely  block  impulses ;  or  it  may  take  the 
form  of  summation,  i.e.,  collect  weak  impulses,  and  combine  them 
into  one  effective  impulse 
before  transmission  to  the 
motor  nerves. 

(2)  The      cell-processes. 
-  The     cell-processes    are 

named  as  follows  :  — 

(a)  Dendrites  or  den- 
drones. 

(6)  Axones,  or  axis  cylin- 
der processes,  named  also 
neuraxones. 

(a)  Dendrites. — These 
processes  are  usually  short, 
and  rather  thick   at   their 
attachment  to  the  cell-body. 
They  have  a  rough  outline, 
diminish  in  calibre  as  they 
extend    further    from    the 

cell-body,  and  branch  in  a  tree-like  manner, 
dendrites  varies.1 

(b)  Axones.  —  The  axone  differs  from  the  dendrite  in  the  fol- 
lowing particulars :  — 

1  The  neurones  in  the  spinal  ganglia  are  exceptional,  having  long  dendrites  and 
comparatively  short  axones. 
D 


;  -No 


FIG.  17.  —  CELL-BODY.  A,  axone.  D,  D, 
dendrites.  Nn,  nucleus  and  nucleolus. 
(Burton-Opitz.) 


The   number   of 


34  ANATOMY  AND   PHYSIOLOGY        [CHAP.  Ill 

(1)  It  is  usually  longer ;  in  some  instances  its  length  may  equal 
half  a  man's  stature. 

(2)  It  has  a  smooth  outline  and  diminishes  in  calibre  very  little. 

(3)  It  gives  off  one  or  more  minute  side  branches  called  col- 
laterals. 

Function  of  the  processes.  —  The  essential  function  of  the  pro- 
cesses is  conduction  of  nerve  impulses  either  to  the  cell-body,  or 
from  the  cell-body.  Those  which  carry  impulses  to  the  cell-body 
are  called  afferent;  those  which  carry  impulses  from  the  cell-body 
are  called  efferent. 

Nerve-fibre.  —  The  term  nerve-fibre  is  only  another  name  for 
the  axone.  These  processes  as  they  extend  away  from  the  cell 
become  surrounded  with  sheaths ;  it  is  therefore  advisable  to  de- 
scribe the  nerve-fibre  separately  as  though  it  were  a  new  subject. 

Nerve-fibres  are  of  two  kinds :  medullated,  or  white  fibres,  and 
non-medullated,  or  gray  fibres. 

Medullated  fibre.  —  If  one  looks  at  a  medullated  nerve-fibre 
under  the  microscope,  it  is  found  to  consist  of  three  parts :  - 

(1)  A  central  core  which  is  a  continuation  of  the  axone;  (2) 
immediately  surrounding  the  axone  is  a  sheath,  or  covering,  of  a 
semi-fluid,  fatty  substance  called  the  myelin  sheath.  It  is  to  this 
fatty  substance  that  medullated  nerve-fibres  owe  their  white 
color.  (3)  External  to  the  myelin  sheath  is  a  thin  membrane 
completely  enveloping  the  nerve-fibre  and  forming  the  outer  cover- 
ing called  the  neurilemma. 

Function  of  the  myelin  sheath.  —  It  is  supposed  that  the 
myelin  sheath  serves  :  (1)  as  a  source  of  nourishment,  (2)  as  a  pro- 
tection, and  (3)  as  a  non-conducting  medium  for  the  fibre.  In  the 
last-mentioned  capacity  it  is  thought  that  this  sheath  prevents 
the  deflection  of  nerve-impulses  from  their  intended  course,  in 
some  such  way  as  the  insulation  of  an  electric  wire  prevents  the 
current  from  taking  a  path  other  than  the  one  desired. 

Nodes  of  Ranvier.  —  At  regular  intervals  along  the  course  of 
a  medullated  nerve-fibre,  the  myelin  sheath  is  interrupted  and 
the  neurilemma  brought  close  to  the  axone.  These  constrictions 
are  the  nodes  of  Ranvier.  Thus  at  each  node  the  nerve-fibre  is 
smaller  in  diameter,  this  change  being  entirely  at  the  expense  of 
the  myelin  sheath,  the  axone  remaining  unchanged.  These  nodes 
are  about  1  mm.  apart  and  the  portion  between  two  consecutive 


CHAP.  Ill] 


NERVE  TISSUE 


35 


NERVE    CELL. 


:DENDRITCS. 


NAKED_ 
AX9NE 


COLLATERAL   BRANCH. 


•MEDULLARY   SHEATH. 


AXONC 

CLOTHED    WITH 

MEDULLARY 

SHEATH. 


AXONC 
CLOTHCD    WITH          ; 

MEDULLARY      / 

SHEATH    AND 
NEURILEMMA. 


—  NEURILEMMA. 


NODES  OF  RANVIER 


AXONE 

CLOTHED    WITH' 
NCURILEMMA. 


NAKED 
AXONE  • 


'TERMINAL   BRANCHES. 


.    FIG.  18.  —  A  NEURONE.     (Gerrish.) 


36  ANATOMY  AND  PHYSIOLOGY        [CHAP.  Ill 

nerves  is  called  an  internode.  In  each  internode  the  neurilemma 
is  seen  to  have  a  nucleus.  Medullated  nerve-fibres  may  be  very 
long,  but  the  diameter  is  very  minute. 

Function  of  the  nodes  of  Ranvier.  —  The  passage  of  blood- 
plasma  into  the  fibre  is  rendered  easier  by  the  absence  of  the  myelin 
sheath  at  the  nodes  of  Ranvier,  and  this  is  thought  to  be  their 
function. 

Non-medullated  fibre.  —  Non-medullated  nerve-fibres  or,  as 
they  are  sometimes  called,  the  fibres  of  Remak,  do  not  differ  in 
any  respect  from  the  medullated  nerve-fibres  save  in  the  absence 
of  the  myelin  sheath,  the  axone  being  directly  invested  by  the 
neurilemma.  Owing  to  the  absence  of  the  myelin  sheath,  the 
non-medullated  fibres  do  not  appear  white,  but  present  a  grayish 
or  yellow  color. 

Collaterals.  —  The  minute  side  branches  of  the  axones  are 
called  collaterals. 

Nerve-endings.  —  Nerve-endings  are  often  of  different  types 
in  accordance  with  their  function  and  may  be  classified  according 
to  the  part  of  the  body  in  which  they  are  found. 

1 .  Nerve-fibres  which  terminate  in  the  brain  or  spinal  cord  split 
up  into  end  arborizations. 

End  arborizations.  —  If  the  nerve-fibre  is  to  terminate  while  still 
lying  in  the  mass  of  the  nervous  system,  its  axone  may  split  up 
at  the  termination  into  a  number  of  short  filaments  called  end 
arborizations,  which  interlock  with  the  dendrites  of  another 
neurone,  or  the  axone  may  send  out  collaterals  which  interlock 
with  dendrites. 

2.  Sensory  nerve-fibres  ending  at  the  periphery  of  the  body 
terminate  in  two  ways  :  — 

(a)  Inter-epithelial  arborizations.  —  This  is  the  most  common 
mode  of  termination  of  sensory  nerves.     The  nerve-fibres  pass  to 
the  surface  either  in  the  skin  or  mucous  membrane ;  the  neurilemma 
and  myelin  sheath  disappear,  the  naked  axone  subdividing  into 
minute  arborizations  that  ramify  between  the  epithelial  cells  of 
the  surface  of  the  body.     This  method  is  the  one  in  which  nerves 
terminate  in  various  glands,  hairs,  teeth,  tendons,  etc. 

(b)  Organules.  —  Some  of  the  highly  complex  special  sensations 
need  very  complex  end  organs  for  their  reception.     These  end 
organs  are  modified  epithelial  cells  and  are  called  organules.     The 


CHAP.  Ill]  NERVE  TISSUE  37 

axone  subdivides  into  arborizations  as  described  above  ;  and  these 
enter  and  terminate  in  the  organules.  The  different  varieties  of 
tactile  corpuscles,  the  organ  of  Corti,  for  the  auditory  nerve,  and  the 
rods  and  cones  of  the  retina  may  be  cited  as  examples  of  organules. 

3.  Motor  nerve-fibres  ending  in  voluntary  muscles  terminate  in 
motor  plates. 

Motor  plates.  —  A  nerve  intended  to  stimulate  a  muscle  to 
activity  terminates  by  a  subdivision  of  the  axone  (the  neurilemma 


FIG.    19.  —  SENSORY   NERVE   TERMINATIONS   IN   STRATIFIED  PAVEMENT 
EPITHELIUM.     (Kirkes.) 

and  myelin  sheath  fading  out),  each  branch  of  the  axone  ending 
in  a  flat  nodule  of  granular  material  lying  on  the  muscle  fibre. 
This  terminal  mass  is  the  motor  plate. 

4.  Motor  nerve-fibres  ending  in  involuntary  muscles  (such  as  in 
the  viscera)  terminate  in  a  plexus. 

Plexus.  —  The  nerve-fibres  which  are  distributed  to  the  viscera 
are  non-medullated,  and  near  their  terminations  each  one  divides 
into  a  number  of  branches  which  arborize  with  each  other  and 
form  a  network  or  plexus.  From  this  plexus  smaller  branches  are 
given  off,  these  subdivide  to  form  fibrils,  and  the  fibrils  terminate 
on  the  surface  of  the  muscle  cells. 

Formation  of  nerves. — The  nerve-fibre  of  each  neurone  is,  as 
has  been  described,  of  microscopic  diameter,  but  when  a  number  of 
these  nerve-fibres  are  bound  together  in  a  bundle  we  have  the  plainly 
visible  nerves,  such  as  are  seen  in  dissections  of  the  body.  Between 
the  individual  nerve-fibres  is  a  small  amount  of  connective  tissue 
which  serves  not  only  to  bind  the  fibres  together  into  bundles,  or 
funiculi,  but  also  to  carry  to  or  from  the  fibres  the  blood-vessels 
and  the  lymphatics  necessary  for  their  nutrition.  Connective 
tissue  also  surrounds  these  bundles  in  the  form  of  a  sheath. 


38  ANATOMY  AND  PHYSIOLOGY        [CHAP.  Ill 

Although  the  nerves  branch  frequently  throughout  their  course, 
and  these  branches  often  meet  and  fuse  with  one  another,  or  with 
the  branches  of  other  nerves,  yet  each  axone  always  remains  quite 
distinct.  The  nerve  is  thus  merely  an  association  of  individual 
fibres  which  have  very  different  activities  and  which  may  function 

ARTERY 

VEIN 


NERVE  FIBRES 

ARTERY 

FIG.  20.  —  TRANSVERSE  SECTION  or  THE  SCIATIC  NERVE  OF  A  CAT  ABOUT  X  100. 
This  nerve  consists  of  eight  bundles  (funiculi)  of  nerve-fibres.  Each  bundle  has 
its  own  wrappings  and  all  the  bundles  are  embedded  in  connective  tissue  in  which 
arteries,  veins,  and  fat  cells  can  be  seen. 

entirely  independent  of  one  another.  Perhaps  the  best  idea  of 
the  arrangement  of  nerves  in  a  trunk  can  be  obtained  from  a  cross 
section  of  a  nerve  such  as  is  seen  in  Fig.  20. 

Gray  and  white  matter.  —  The  cell-bodies  of  neurones  and  many 
of  their  processes  are  grouped  together  into  what  we  call  gray 
matter.  Gray  matter  is  found  in  the  cortex  of  the  brain,  the 
core  of  the  spinal  cord,  and  making  up  the  ganglia.  Experiments 
have  shown  that  various  activities  of  the  body  are  controlled  from 
certain  areas  in  the  gray  matter.  For  instance,  the  rate  of  res- 
piration is  controlled  by  an  area  in  the  medulla  oblongata  or  spinal 
bulb,  and  odor  is  interpreted  from  a  certain  region  in  the  cerebrum. 
Regions  of  gray  matter  which  function  in  this  way  we  call  centres, 
and  we  speak  of  the  respiratory  centre,  the  olfactory  centre,  etc. 
The  medullated  processes  of  cell-bodies  are  grouped  together,  as 
described,  into  nerves,  and  these  nerves  constitute  what  we  call 
white  matter. 


CHAP.  Ill] 


NERVOUS  SYSTEM 


39 


Nervous  System 


1.  Central  Nervous 
System 


Brain 


THE  NERVOUS  SYSTEM 

Nerve  tissue  enters  into  the  structure  of  all  parts  of  the  ner- 
vous system.  In  other  words,  the  nervous  system  exclusive  of 
the  supporting  and  connecting  tissues  is  simply  an  aggregation  of 
millions  of  neurones  or  nerve-cells.  Regionally  considered,  the 
nervous  system  presents  itself  as  (1)  the  central  nervous  system 

and  (2)  the  peripheral  nervous  system. 

Cerebrum. 
Cerebellum. 
Pons  Varolii. 
Medulla  Oblongata. 
Spinal  cord. 

f  Cranial  nerves. 
2.  Peripheral  Nervous     Spinal  nerves< 

[  Sympathetic  nervous  system. 

Central  nervous  sys- 
tem.—  The  central  ner- 
vous system  consists  of 
the7 brain  and  spinal  cord. 
The  general  arrangement 
of  this  system  is  shown  in 
Fig.  21.  The  nerves  con- 
nected with  the  brain  are 
the  cranial,  those  con- 
nected with  the  spinal  cord 
are  the  spinal  nerves,  and 
both  of  these  systems  of 
nerves  together  are  called 
the  cerebrospinal  nerves, 
in  contrast  to  the  sym- 
pathetic nerves. 

Ganglion.  —  The  term 
ganglion  is  used  to  de- 
scribe a  collection  of  neu- 
rones outside  the  central 
nervous  system.  Ganglia 
appear  in  the  course  of 
the  cranial  and  spinal 
nerves  and  form  the  chief 
mass  of  the  sympathetic 
system. 


FIG.  21.  —  DIAGRAM  ILLUSTRATING  THE  BRAIN, 
SPINAL  CORD,  AND  SPINAL  NERVES. 


40 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  Ill 


Sympathetic  system.  —  The  sympathetic  or  autonomic  ner- 
vous system  consists  of  innumerable  ganglia  and  nerves  distributed 
very  widely  throughout  the  body,  chiefly  to  the  viscera.  It  is 
closely  connected  with  the  central  nervous  system  through  bridges 
of  nerves,  known  as  the  white  and  gray  communicating  rami. 

Properties  of  nerve  tissue.  —  Nerve  tissue  is  the  most  highly 
specialized  tissue  in  the  body.  It  possesses  the  following  marked 
characteristics :  (1)  irritability  or  the  power  to  respond  to  stimu- 
lation, and  (2)  conductivity  or  the  power  to  transmit  the  stimulus 
or  nerve  impulse  to  the  muscles,  viscera,  etc. 

For  a  fuller  discussion  of  the  Nervous  System  see  Chapter  XIX. 


SUMMARY 

The  human  body  is  an  enormous  aggregate  of  cells.  A  cell  is  a  minute 
portion  of  protoplasm,  sometimes  enclosed  in  a  cell-wall.  May  contain 
a  nucleus  which  in  turn  often  contains  nucleoli. 


Cell 


Life 

activities 
in  cells 


Protoplasm 
(living) 


Metaplasm 
(not  living) 

1.  Support. 


Cytoplasm  —  protoplasm  surrounding  nu- 
cleus. 

Nucleus  —  protoplasm  inside  the  nuclear 
membrane.  Contains  chromatin  and 
achromatin. 

Centrosome  —  found  in  actively  multiply- 
ing cells. 

Food. 

Wastes. 

Storage  products. 


2.  Respiration 


3.  Metabolism 


4.  Motion 


Combines  with  oxy gen  =  oxidation. 
Liberates  heat. 
Carbon  dioxide  formed. 
Anabolism  =  building-up  process. 
Katabolism  =  breaking-down  process. 
(a)  Amreboid  movement. 
(6)  Ciliary  movement. 

5.  Circulation  —  Streaming  of  the  protoplasm,  within  the 

limits  of  the  cell. 

6.  Excretion  —  Discharge  of  waste  substances. 

7.  Irritability  —  Ability  to  respond  to  stimuli. 

(a)  Simple,  direct  division. 

(b)  Indirect  division  or  mitosis. 


8.  Cell  division 


CHAP.  Ill] 


SUMMARY 


41 


Voluntary  muscle  cell  an  inch  long. 
Size     Processes  of  nerve  cells  may  be  three  feet  or  more. 

Red  blood  cell  ^Vrr  inch  in  diameter. 
Differences  [  Pressure, 

in  cells       j  Form  depends  on  <  Movements  of  cell. 

[  Growth  and  differentiation. 

Chemical  composition  —  dependent  on  special  work  of  cell. 
Function  —  assist  in  work  of  tissue  of  which  it  forms  a  part. 
Tissues  —  are  made  up  of  a  collection  of  cells  of  like  substance,  with 

more  or  less  intercellular  substance  between  the  cells. 
Organs  —  are  made  up  of  two  or  more  tissues  associated  to  perform  a 

common  function. 

System.  —  A  group  of  organs  set  apart  to  perform  some  special  function. 
Eight  systems  are  found  in  the  human  body. 
Skeletal. 
Respiratory. 
Alimentary. 
Muscular. 

Classification   j  1.  Epithelial, 
of  tissues       I  2.  Nerve. 

(a)  Impregnation. 

(6)  Multiplication  of  cells. 

Ectoderm 


Vascular. 
Excretory. 
Nervous. 
Reproductive. 

3.  Connective. 

4.  Muscular. 


Origin  of 
tissues 


(c) 


Formation 

of 
Blastoderm 


Mesoderm 


Entoderm 


Epidermis. 
Nervous  system. 
Circulatory  system. 
Most  of  the  genito-urinary 

system. 
Muscles. 

Connective  tissues. 
Lining  of  respiratory  tract. 
Lining  of  alimentary  tract. 
Liver,  pancreas,  and  other 

glands. 
Epithelial  —  a  tissue  of  cells  and  little  intercellular  substance. 

Pavement  or  scaly. 
Columnar. 
Ciliated. 

Transitional,  consisting  of  2  or  3  layers. 
Stratified,  consisting  of  many  layers. 
Protection. 
Motion. 
Absorption. 
Secretion. 
Special  sensation. 

Nerre  tissue.  —  A  tissue  of  differentiated  cells  called  neurones  held  in 
place  by  neuroglia. 


Classification 
of  epithelial 
tissue 


Function 


Simple,  consisting  of  a  single 
layer 


42 


ANATOMY  AND  PHYSIOLOGY        [CHAP.  Ill 


Neurone 


Cell- 
processes 


Dendrites 


Axone 


Nerve-fibre 


Nodes  of 
Ranvier 


1.  Source  of  nour- 
ishment 

2.  Non-conducting 
medium. 


Cytoplasm  surrounds  nucleus. 

Cell-body       Nucleus  may  or  may  not  contain  nucleolus. 
f  Nutritive  centre. 

Function  ,  [Inhibition. 

[  Modifies  impulses  {  Q  . 

[  Summation. 

Usually  short,  break  up  into  many 
branches.  Rough  outline  —  di- 
minish in  calibre.  May  be  one, 
or  many. 

f  Long,    smooth    outline,    diminishes 
\     very  little.     Gives  off  collaterals. 
Function  is  conduction  of  nerve  impulses  either 
to  the  cell-body    (afferent),  or  from  the  cell- 
body  (efferent). 

I  Axone 
Myelin  sheath  —  function 
Neurilemma 

AT  j  n  4.  j    f  Axone. 

Non-medullated  \  ,T      ., 

[  Neurilemma. 

Ring-like  constrictions  in  medullated  fibres,  due  to  absence 

of  myelin  sheath. 
Function  —  Passage    of    bipod-plasma    to    fibre    rendered 

easier. 
Collaterals.  —  Minute  side  branches  given  off  from  axones. 

1.  End  arborizations  —  terminations  in  brain  or  cord. 

Terminations  of  sensory 
fibres  at  the  periphery 
of  the  body. 

3.  Motor  plates  —  terminations   of  motor  nerve-fibres   in 

voluntary  muscle. 

4.  Plexus  —  terminations  of  motor  nerve-fibres  in  involun- 

tary muscle. 

Bundles  of  nerve-fibres  bound  together  to  make  funiculi. 
Nerves         {  Funiculi  bound  together  to  make  nerve-trunks. 

Connective  tissue  surrounds  funiculi  and  nerve-trunks. 

Cell-bodies  of  neurones  and  many  of  their 
processes. 

Cortex  of  brain. 
Gray  matter      Found  in    Core  of  spinal  cord. 

Ganglia. 
Centres  —  Groups  of  neurones  exercising 

control  over  some  definite  function. 
Myelinated   processes    of    cell-bodies  are 
White  matter  J      grouped    together    into    nerves,    and 
these  constitute  white  matter. 


Nerve- 
endings 


2. 


Inter-epithelial  arborizations 
Organules 


Classification 
of  nerve 
tissue 


CHAP.  Ill] 


Nervous 
system 


SUMMARY 


1.  Central  nervous  system 


2.  Peripheral  nervous  system 


43 


Cerebrum. 
Cerebellum. 
Pons  Varolii. 
Medulla  oblon- 


Brain 


Spinal  cord. 
Cranial  nerves 
Spinal  nerves 


Sympathetic    nervous 
^     system. 

Properties       of  J  1.  Irritability  or  the  power  to  respond  to  stimulation, 
nerve  tissue     I  2.  Conductivity  or  the  power  to  transmit  stimuli. 


CHAPTER  IV 

CONNECTIVE  TISSUES:   AREOLAR,  FIBROUS,  ELASTIC,  ADIPOSE, 
RETICULAR,    NEUROGLIA,    CARTILAGE,   BONE 

FOLLOWING  the  classification  of  tissues  we  have  adopted,  the 
next  group  to  be  studied  is  that  known  as  the  connective  tissue 
group'. 

Our  description  of  epithelial  tissue  was  briefly  this :  a  skin  or 
membrane  formed  of  cells,  which  cells  may  be  of  a  variety  of 
shapes,  and  be  arranged  in  one  or  more  layers.  It  is  distinctly 
a  tissue  of  cells  with  very  little  of  what  we  call  intermediate  or 
intercellular  substance  lying  between  the  cells.  Connective 
tissue  differs  from  epithelial  tissue  in  having  a  great  deal  of  inter- 
cellular substance  lying  between  the  cells.  It  may  be  interesting 
to  note  that  in  this  form  of  tissue,  the  intercellular  substance  is 
supposed  to  develop  from  the  cells. 

CONNECTIVE  TISSUE  GROUP 

These  tissues  differ  considerably  in  their  external  characteristics, 
but  are  alike  (1)  in  that  they  all  serve  to  connect  and  support  the 
other  tissues  of  the  body ;  (2)  they  l  are  all  developed  from  the 
mesoderm ;  (3)  the  cellular  element  is  at  a  minimum,  and  the  in- 
tercellular material  is  at  a  maximum ;  (4)  they  originate  no  action 
but  are  acted  upon  by  the  other  tissues.  We  may  therefore  group 
them  together  as  follows  :  — 

1.  Areolar  tissue.  5.   Reticular  tissue. 

2.  Fibrous  tissue.  0.   Neuroglia. 

3.  Elastic  tissue.  7.    Cartilage. 

4.  Adipose  tissue.  8.   Bone  or  osseous  tissue. 

Areolar  tissue.  —  This  tissue  appears  to  be  composed  of  a  mul- 
titude of  fine  threads  or  films,  called  fibres.  Viewed  with  a 
microscope,  these  fibres  are  seen  to  be  principally  made  up  of  wavy 

1  With  one  exception,  neuroglia.     See  page  50. 
44 


CHAP.  IV] 


CONNECTIVE  TISSUES 


45 


bundles  of  exquisitely  fine,  transparent,  white  fibrils,  and  these 
bundles  intersect  in  all  directions.  Mixed  with  the  white  fibres 
are  a  certain  number  of  yellow  elastic  fibres,  which  do  not  form 
bundles,  and  have  a  straight  instead  of  a  wavy  outline.  Between 
these  fibres  are  open  spaces,  called  areolse.1  These  spaces  contain 
a  semifluid  ground  substance  or  matrix  and  communicate  freely 


VACUOLATED    CELL   f  WHITE   FIBRES 


IANCHING 

AMELLAR 


FIG.  22.  —  SUBCUTANEOUS  AREOLAR  TISSUE  FROM  A  YOUNG  RABBIT.  (Highly 
magnified.)  The  white  fibres  are  in  wavy  bundles,  the  elastic  fibres  form 
an  open  network.  (Schafer.) 

with  one  another.  Lying  in  the  areolse  between  the  bundles  of 
fibres  are  seen  the  tissue-cells,  of  which  there  are  many  varieties. 

If  we  make  a  cut  through  the  skin  of  some  part  of  the  body 
where  there  is  no  subcutaneous  fat,  as  in  the  upper  eyelid,  and 
proceed  to  raise  it  from  the  parts  lying  beneath,  we  observe  that 
it  is  loosely  connected  to  them  by  a  soft,  filmy  substance  of  con- 
siderable tenacity  and  elasticity.  This  is  areolar  tissue. 

Function.  —  Areolar  tissue  forms  web-like  binding  and  support- 
ing material  and  serves  to  connect  and  insulate  entire  organs. 
It  is  one  of  the  most  general  and  most  extensively  distributed  of 
the  tissues.  It  is,  moreover,  continuous  throughout  the  body, 

1  Areola  is  the  Latin  word  for  "a  small  space."  Areolar  tissue  gets  its  name 
from  appearing  full  of  minute  spaces. 


46 


ANATOMY  AND  PHYSIOLOGY        [CHAP.  IV 


and  from  one  region  it  may  be  traced  without  interruption  into 
any  other,  however  distant,  —  a  fact  not  without  interest  in  practi- 
cal medicine,  seeing  that  in  this  way  air,  water,  pus,  and  other 
fluids,  effused  into  the  areolar  tissue,  may  spread  far  from  the  spot 
where  they  were  first  introduced  or  deposited. 

Fibrous  tissue.  —  This  tissue  is  intimately  allied  in  structure  to 
the  areolar  tissue.  It  consists  almost  wholly  of  wavy  white  fibres, 
which  cohere  very  closely  and  are  arranged  side  by  side  in  bundles 
which  have  an  undulating  outline.  The  spaces  between  the  bun- 
dles are  occupied  by  cells  arranged  in  rows,  but  the  cells  are 

not  a  prominent  feature  of  this 
tissue.  The  fibres  may  be  some 
inches  long,  do  not  branch,  and 
confer  a  distinctly  fibrous  aspect 
on  the  parts  which  they  compose. 

Fibrous  tissue  is  white,  with  a 
peculiarly  shining,  silvery  aspect. 
It  is  exceedingly  strong  and  tough, 
yet  perfectly  pliant;  but  it  is  al- 
most devoid  of  extensibility  and  is 
very  sparingly  supplied  with  nerves 
and  blood-vessels. 

Function.  —  Fibrous  tissue  is  met 
with  in  the  form  of :  — 

(1)  Ligaments.  —  Ligaments    are 
FIG.  23. -FIBROUS  TISSUE,  FROM     t          flexible  bands,  or  capsules, 

THE   LONGITUDINAL   SECTION  OF  A 

TENDON.     The  spaces  between  the  of  fibl'OUS   tissue   that    help   to   hold 

bundles  of  fibres  are  occupied   by  ,1       i  ,1  ,1       •    •    , 

rows  of  cells.     (Gegenbauer.)  the  bones  together  at  the  joints. 

(2)  Tendons  or  sinews.  —  Tendons 

are  white  glistening  cords  or  bands  which  serve  to  attach  the 
muscles  to  the  bones.     They  are  usually  composed  of  white  fibres, 
but  may  contain  some  yellow  fibres. 

(3)  Aponeuroses.  —  Aponeuroses  are  flat,  wide  bands  of  fibrous 
tissue  which  serve  to  connect  one  muscle  with  another. 

(4)  Protecting  sheaths  or  membranes.  —  Fibrous  tissue  is  found 
investing  and  protecting  different  organs  of  the  body.     Examples 
—  heart  and  kidneys. 

(5)  Fascia.  —  The  word  fascia  means  a  barid  or  bandage.     It  is 
most  frequently  applied  to  sheets  of  fibrous  membrane  which  are 


CHAP.  IV]  CONNECTIVE  TISSUES  47 

wrapped  around  muscles,  and  serve  to  hold  them  in  place.  Fasciae 
are  divided  into  two  groups,  which  are  associated  with  the  skin 
and  the  muscles.  They  are  called  :  — 

a.  Superficial. 

b.  Deep. 

a.  Superficial  fascice.  — The  subcutaneous  areolar  tissue,  which 
forms  a  nearly  continuous  covering  beneath  the  skin,  is  classed  as 
superficial  fascia.     It  varies  in  thickness,  and  usually  permits 
free  movement  of  the  skin  on  the  subjacent  parts. 

The  fascia  covering  the  palms  of  the  hands  is  named  palmar 
fascia,  and  the  fascia  covering  the  soles  of  the  feet  is  named  plantar 
fascia.  The  palmar  and  plantar  fasciae  are  much  thicker,  stronger, 
and  more  closely  attached  than  the  superficial  fasciae  in  other  parts 
of  the  body. 

b.  Deep  fascice.  —  The  deep  fasciae  are  sheets  of  white,  flexible 
fibrous  tissue,  employed  to  envelop  and  bind  down  the  muscles, 
also  to  separate  them  into  groups.     (See  page  98.)     The  term 
fascia,  unless  limited  by  an  adjective,  is  usually  employed  to  desig- 
nate the  deep  fascice.     Subcutaneous  areolar  tissue  is  rarely  called 
by  the  name  fascia,  though  it  is  correctly  classed  as  such. 

Elastic  tissue.  —  In  elastic  tissue  the  wavy  white  bundles  are 
comparatively  few  and  indistinct,  and  there  is  a  proportionate 
development  of  the  elastic  fibres.  When  present  in  large  numbers, 
they  give  a  yellowish  color  to  the  tissue.  This  form  of  connective 
tissue  is  extensile  and  elastic  in  the  highest  degree,  and  wherever 
located,  does  such  work  as  India  rubber  would  do.  It  is  not  so 
strong  as  the  fibrous  variety,  and  breaks  across  the  direction  of 
its  fibres  when  forcibly  stretched. 

Function.  —  Elastic  tissue,  being  extensile  and  elastic,  has  a 
most  important  use  in  assisting  muscular  tissue,  and  so  lessening 
the  wear  and  tear  of  muscle.  It  is  found  :  — 

(1)  Between  the  transverse  processes  of  the  vertebrae  in  elastic 
bands.     (Ligamenta  flava .)     (See  page  76.)' 

(2)  In    the    walls    of    the    blood-vessels    (especially    arteries), 
bronchial  tubes,  and  vocal  cords. 

(3)  Entering  into  the  formation  of  the  lungs  and  uniting  the 
cartilages  of  the  larynx. 

These  three  varieties  of  connective  tissue  (areolar,  fibrous, 
elastic)  agree  closely  with  one  another  in  elementary  structure. 


48  ANATOMY  AND   PHYSIOLOGY        [CHAP.  IV 

It  is  the  different  arrangement  of  the  cells  and  fibres,  and  the  rel- 
ative proportion  of  one  kind  of  fibre  to  the  other,  that  gives 
them  their  different  characteristics.  They  are  used  for  purely 
mechanical  purposes. 

Adipose  tissue.  —  When  fat  begins  to  be  formed,  it  is  deposited 
in  tiny  droplets  l  in  some  of  the  cells  of  the  areolar  tissue ;  these 
droplets,  increase  in  size,  and  eventually  run  together  so  as  to  form 
one  large  drop  in  each  cell.  By  further  deposition  of  fat  the  cell 
becomes  swollen  out  to  a  size  far  beyond  that  which  it  possessed 


FIG.  24. — A  FEW  FAT  CELLS  FROM  THE  MARGIN  OF  A  FAT  LOBULE.  (Very 
highly  magnified.)  /.  g.,  fat  globule  distending  a  fat  cell;  n,  nucleus;  m,  proto- 
plasmic envelope  of  the  fat  cell;  c,  capillary  vessel;  v,  vr^ule;  c.t.,  connective- 
tissue  cell ;  the  fibres  of  the  connective  tissue  are  not  shown.  (Schafer.) 

originally,  until  the  protoplasm  remains  as  a  delicate  envelope 
surrounding  the  fat  drop.  The  nucleus  is  crowded  off  to  one  side 
and  attached  to  the  cell  membrane.  As  these  cells  increase  in 
number  they  collect  into  small  groups  or  lobules,  which  lobules 
are  for  the  most  part  lodged  in  the  meshes  of  the  areolar  tissue, 
and  are  also  supported  by  a  fine  network  of  blood-vessels.  This 
fatty  tissue  exists  very  generally  throughout  the  body,  accompany- 
ing the  still  more  widely  distributed  areolar  tissue  in  most  parts, 
though  not  in  all,  in  which  the  latter  is  found.  Still,  its  distribu- 

1  The  contents  of  the  fat  cells  of  adipose  tissue  are  fluid  during  life,  as  the  normal 
temperature  of  the  body  is  considerably  above  the  melting  point  of  the  mixture 
of  fats  found  there. 


CHAP.  IV]  CONNECTIVE  TISSUES  49 

tion  is  not  uniform,  and  there  are  some  situations  in  which  it  is 
collected  more  abundantly.  This  tissue  is  found  chiefly  :  — 

(1)  Underneath  the  skin,  in  the  subcutaneous  layer. 

(2)  Beneath  the  serous  membranes  or  in  their  folds. 

(3)  Collected  in  large  quantities  around  certain  internal  organs, 
especially  the  kidneys,  helping  to  hold  them  in  place. 

(4)  Filling  up  furrows  on  the  surface  of  the  heart. 

(5)  As  padding  around  the  joints. 

(6)  In  large  quantities  in  the  marrow  of  the  long  bones. 
Function.  —  Adipose  tissue  serves  several  important  purposes. 

(1)  It  constitutes  an  important  reserve  fund,  which  can  be 
returned  to  the  cells  by  the  blood  and  oxidized,  thus  producing 
energy.  (2)  It  serves  as  a  jacket  or  covering  under  the  skin, 
and  being  a  non-conductor  of  heat,  prevents  the  too  rapid  loss  of 
heat  through  the  skin.  (3)  It  is  an  admirable  packing  material, 
and  serves  to  fill  up  spaces  in  the  tissues,  and  thus  affords*  sup- 
port for  delicate  structures  such  as  blood-vessels  and  nerves. 

Reticular  or  retiform 1  tissue.  —  This   variety   of   connective 
tissue  consists  of  a  close  network  of  white  fibres  with  few,  if  any, 


FIG.  25.  —  RETIFORM  TISSUE  FROM  A  LYMPH  NODE,     r,  r,  r,  represent  open 
meshes  of  this  tissue.     (Quain.) 

yellow  fibres.  The  meshes  of  the  network  are  small  and  close  in 
some  parts,  more  open  and  like  areolar  tissue  in  other  parts.  The 
fibres  are  nearly  covered  by  fibrous  tissue  cells  in  the  form  of 
broad,  thin  plates  wrapped  around  them. 

Function.  —  Reticular  tissue  forms  a  fine  framework  in  many 
organs,  e.g.  the  muscles. 

1  Reticulum  (from  the  Latin  reticulum,  "a  small  net ") .     Resembling  a  small  net. 
E 


50  ANATOMY  AND   PHYSIOLOGY        [CHAP.  IV 

Lymphoid  or  adenoid 1  tissue.  —  This  is  reticular  tissue  in 
which  the  meshes  of  the  network  are  occupied  by  lymph 
corpuscles.  This  is  the  most  common  condition  of  retiform 
tissue.  • 

Lymphoid  tissue  forms  the  principal  part  of  the  substance  of 
the  spleen  and  lymph  nodes.  It  also  -enters  into  the  composition 
of  the  tonsils  and  some  of  the  intestinal  glands. 

Neuroglia.  —  This  is  a  peculiar  form  of  connective  tissue  found 
only  in  the  nervous  system.  Unlike  the  other  connective  tissues 
it  is  derived  from  the  ectoderm,  not  the  mesoderm.  It  consists 
of  cells  called  glia  cells  that  give  off  numerous  fine  processes  which 
extend  in  every  direction  and  intertwine  among  the  nerve  cells 
and  processes,  forming  a  supporting  network. 

Cartilage.  —  This  is  the  well-known  substance  called  gristle. 
Although  cartilage  can  be  readily  cut  with  a  sharp  knife,  it  is  never- 
theless of  very  firm  consistence,  but  at  the  same  time  highly  elastic, 
so  that  it  readily  yields  to  extension  or  pressure,  and  immediately 
recovers  its  original  shape  when  the  constraining  force  is  with- 
drawn. When  a  very  thin  section  is  examined  with  a  microscope, 
it  is  seen  to  consist  of  nucleated  cells  disposed  in  small  groups  in 
a  mass  of  intercellular  substance.  This  intercellular  substance  is 
sometimes  transparent,  and  to  all  appearances  structureless; 
sometimes  it  is  pervaded  with  white  fibres  and  sometimes  with 
yellow  fibres.  According  to  the  amount  and  texture  of  the  in- 
tercellular substance,  we  distinguish  three  principal  varieties :  — 

(1)  Hyaline  or  true  cartilage. 

(2)  White  fibro-cartilage. 

(3)  Yellow  or  elastic  fibro-cartilage. 

Hyaline  cartilage.  —  This  variety  is  named  from  the  Greek 
word  for  glass.  A  comparatively  small  number  of  cells  are  em- 
bedded in  an  abundant  quantity  of  intercellular  substance  which 
has  the  appearance  of  ground  glass. 

1.  Hyaline  cartilage  covers  the  ends  of  the  bones  in  the  joints, 
where  it  is  known  as  articular  cartilage. 

2.  Hyaline  cartilage  forms  the  rib  cartilages,  where  it  is  known 
as  costal  cartilage. 

In  both  these  situations  the  cartilages  are  in  immediate  connec- 

1  Adenoid  (from  the  Greek  aden,  "a  gland,"  and  eidos  or  "resemblance"). 
Pertaining  to  or  resembling  a  gland. 


CHAP.  IV] 


CONNECTIVE  TISSUES 


51 


tion  with  bone,  and  may  be  said  to  form  part  of  the  skeleton, 
hence  are  frequently  described  as  skeletal  cartilages. 

Function.  —  The  articular  cartilages,  in  covering  the  ends  or 
surfaces  of  bones  in  the  joints,  provide  these  harder  parts  with  a 
thick,  springy  coating,  which  breaks  the  force  of  concussion,  and 
gives  ease  to  the  motion  of  the  joint.  The  costal  cartilages,  in 
forming  part  of  the  solid  framework  of  the  thorax  or  chest,  impart 
elasticity  to  its  walls.  Hyaline  cartilage  also  enters  into  the  for- 
mation of  the  nose,  ear,  larynx, 
and  trachea.  It  strengthens  the 
substance  of  these  parts  without 
making  them  unduly  rigid,  main- 
tains their  shape,  keeps  open  the 
passages  through  them  where  such 
exist,  and  gives  attachment  to* 
moving  muscles  and  connecting 
ligaments. 

White  fibro-cartilage.  —  The  in- 
tercellular substance  is  pervaded 
with  bundles  of  white  fibres,  be- 
tween which  are  scattered  cartilage 
cells.  It  closely  resembles  white 
fibrous  tissue. 

White  fibro-cartilage  is  found 
joining  bones  together,  the  most 
familiar  instance  being  the  flat, 
round  plates  or  discs  of  fibro- 
cartilage  connecting  the  bones  of  protoplasmic  cell ;  n,  nucleus. 

the   spine  and   the   pubic   bones. 

In  these  cases  the  part  in  contact  with  the  bone  is  always  hyaline 

cartilage,  which  passes  gradually  into  the  fibro-cartilage. 

Function.  —  It  serves  as  a  strong,  flexible,  connecting  material 
between  bones  and  is  found  wherever  great  strength  combined 
with  a  certain  amount  of  rigidity  is  required. 

Yellow,  or  elastic,  fibro-cartilage.  —  The  intercellular  substance 
is  pervaded  with  yellow  elastic  fibres  which  form  a  network. 
In  the  meshes  of  the  network  the  cartilage  cells  are  found. 

Yellow,  or  elastic,  fibro-cartilage  is  found  in  the  epiglottis,  car- 
tilages of  the  larynx,  Eustachian  tube,  and  external  ear. 


'  RENAVDOT  S.SAllf 

FIG.  26.  —  ARTICULAR  HYALINE 
CARTILAGE  FROM  THE  FEMUR  OF  AN 
Ox.  s,  intercellular  substance;  p, 

(Ran- 


52  ANATOMY  AND   PHYSIOLOGY        [CHAP.  IV 

Function.  —  It  strengthens  and  maintains  the  shape  of  these 
organs,  and  yet  allows  of  a  certain  amount  of  elasticity. 

Cartilage  is  not  supplied  with  nerves,  and  very  rarely  with 
blood-vessels.  Being  so  meagrely  supplied  with  blood,  the  vital 
processes  in  cartilage  are  very  slow,  and  when  a  portion  of  it  is 
absorbed  in  disease  or  removed  by  the  knife,  it  is  regenerated 
very  slowly.  A  wound  in  cartilage  is  usually  healed  by  connec- 
tive tissue  proper,  which  may  or  may  not  become  gradually  trans- 
formed into  cartilage.  Nearly  all  cartilages  receive  their  nourish- 
ment from  the  perichondrium,  a  moderately  vascular  fibrous  mem- 
brane which  covers  them. 

Bone,  or  osseous,  tissue.  —  Bone  is  connective  tissue  in  which 
the  intercellular  substance  derived  from  the  cells  is  rendered 
hard  by  being  impregnated  with  mineral  salts. 

The  mineral,  or  earthy,  substance  which  is  deposited  in  bone, 
and  which  makes  it  hard,  consists  chiefly  of  phosphate  of  calcium, 
with  about  a  fifth  part  of  carbonate  of  calcium,  and  a  small  por- 
tion of  other  salts. 

The  organic,  or  soft,  matter  consists  chiefly  of  blood-vessels  and 
connective  tissue,  and  may  be  almost  entirely  resolved  into  gela- 
tine by  boiling. 

It  is  possible  to  separate  each  of  these  substances.  The  min- 
eral matter  may  be  removed  by  soaking  a  bone  in  dilute  acid  for 
several  days.  The  result  will  be  a  tough,  flexible,  elastic  substance, 
consisting  only  of  organic  matter.  The  shape  of  the  bone  will  be 
preserved,  but  the  specimen  will  be  so  free  from  stiffness  that  it 
may  be  tied  in  a  knot. 

The  organic  matter  may  be  driven  off  by  heat.  As  before,  the 
shape  of  the  bone  will  be  preserved.  The  specimen  will  consist 
only  of  mineral  matter,  will  appear  white,  rigid,  and  so  brittle  it 
can  be  crushed  between  the  fingers. 

Amount  of  organic  and  inorganic  matter.  —  The  comparative 
amount  of  organic  and  inorganic  matter  found  in  bone  is  dependent 
on  the  age  of  the  individual.  In  the  foetus  the  tissues  that  later 
become  bone  are  either  fibrous  or  cartilaginous.  By  absorption 
of  mineral  substances  from  the  blood,  these  tissues  gradually 
become  ossified.  Thus  it  follows  that  in  youth  the  organic 
matter  is  in  excess.  In  adult  life  the  organic  matter  constitutes 
about  one-third  of  the  weight  of  the  bone,  and  the  inorganic 


CHAP.  IV] 


CONNECTIVE  TISSUES 


53 


matter  two-thirds.     In  old  age  the  amount  of  inorganic  matter 
is  increased. 

Fracture. — The  term  fracture  is  applied  to  the  breaking  of 
a  bone.  As  a  result  of  the  greater  amount  of  organic  matter  in 
the  bones  of  children,  they  are  flexible,  bend 
easily,  and  do  not  break  readily.  In  some 
cases  the  bone  bends  like  a  bough  of  green 
wood.  Some  of  the  fibres  may  break,  but 
not  the  whole  bone,  hence  the  name  green- 
stick  fracture.  It  is  also  true  that  the 
greater  amount  of  inorganic  matter  in  the 
bones  of  the  aged  render  the  bones  more- 
brittle,  so  that  they  break  easily  and  heal 
with  difficulty. 

Rachitis  or  Rickets.  —  In  the  disease 
called  rickets,  quite  common  among  poorly 
nourished  children,  there  is  not  sufficient 
mineral  matter,  so  that  the  bones  are  flexible, 
bend  easily,  and  may  be  permanently  mis- 
shapen. 

Structure  of  Bone.  —  On  sawing  a  bone 
it  will  be  seen  that  in  some  parts  it  is  open 
and  spongy,  whilst  in  others  it  is  dense  and 
close  in  texture,  appearing  like  ivory.  We 
thus  distinguish  two  forms  of  bony  tissue  :  — 

(1)  The  cancellated,  or  spongy. 

(2)  The  dense,  or  compact. 

On  closer  examination,  it  will  be  seen 
that  the  bony  matter  is  everywhere  porous, 
and  that  the  difference  between  the  two 
varieties  of  tissue  arises  from  the  fact  that 
the  compact  tissue  has  fewer  spaces  and 
more  solid  matter  between  them,  while  the 
cancellated  has  larger  cavities  and  more  BoNE- 
slender  intervening  bony  partitions.  In  all  bones  the  compact 
tissue  is  the  stronger;  it  lies  on  the  surface  of  the  bone  and 
forms  an  outer  shell  or  crust,  whilst  the  lighter,  spongy  tissue  is 
contained  within.  The  shafts  of  the  long  bones  are  made  up  al- 
most entirely  of  the  compact  substance,  except  that  they  are 


FIG.     27.  —  VERTICAL 
SECTION     OF     A     LONG 


54 


ANATOMY  AND  PHYSIOLOGY        [CHAP.  IV 


OSTCOQCNET 
CELLS 


LAMELUC 

LACUN/E 

CANALICUL 

HAVERSIAN 

CANAL 


PLETC 
HAVERSIAN 
SYSTEM 


FIG.  28.  —  DIAGKAM  or  THE  STRUCTURE  OF  OSSEOUS  TISSUE.  A  small  part  of  a 
transverse  section  of  the  shaft  of  a  long  bone  is  shown.  At  the  uppermost  part 
is  the  periosteum  covering  the  outside  of  the  bone ;  at  the  lowermost  part  is  the 
endosteum  lining  the  marrow  cavity.  Between  these  is  the  compact  tissue  con- 
sisting largely  of  a  series  of  Haversian  systems,  each  being  circular  in  outline 
and  perforated  by  a  central  canal.  In  the  first  one  is  shown  only  the  area  occupied 
by  a  system ;  in  the  second  is  seen  the  concentric  arrangement  of  the  lamellae ; 
in  the  others,  respectively,  canaliculi ;  lacunae  ;  lacunas  and  canaliculi ;  the  contents 
of  the  canal,  artery,  vein,  lymphatic,  and  areolar  tissue ;  lamellae,  lacunae,  and 
canaliculi ;  and  finally  all  of  the  structures  composing  a  complete  system.  Between 
the  systems  are  circumferential  and  intermediate  lamella?,  only  a  few  of  which  are 
represented  as  lodging  lacunae,  though  it  is  to  be  understood  that  lacunaa  are  in  all 
parts.  The  periosteum  is  seen  to  be  made  up  of  a  fibrous  layer  and  a  vascular 
layer,  and  to  have  upon  its  attached  surface  a  stratum  of  cells.  From  the  fibrous 
layer  project  inward  the  rivet-like  fibres  of  Sharpey.  (Gerrish.) 


CHAP.  IV]  CONNECTIVE  TISSUES  55 

hollowed  out  to  form  a  central  canal,  —  the  medullary  canal,— 
which  has  a  fibrous  lining  called  endosteum,  and  contains  marrow. 

The  hard  substance  of  both  varieties  is  arranged  in  bundles  of 
bony  fibres,  or  lamellce  (layers). 

Cancellated  bone.  —  In  cancellated  bone  the  lamellae  join  and 
meet  together  so  as  to  form  a  structure  resembling  lattice-work 
(cancelli),  whence  this  tissue  receives  its  name.  In  the  interstices 
of  this  kind  of  bone  we  find  the  blood-vessels  supported  by  the 
marrow. 

Compact  bone.  —  In  compact  bone  the  lamellae  are  usually  ar- 
ranged in  rings  around  canals,  —  Haversian  canals,  —  which  carry 


- 

CANALICULI  T* 


HAVERSIAN  CANAL 


-JUNCTION  OF  TWO 
HAVERSIAN  SYSTEMS 


Fn;.  29.  —  TRANSVERSE  SECTION  OF  OSSEOUS  TISSUE. 

blood-vessels  in  a  longitudinal  direction  through  the  bones.  The 
canals  branch  freely  from  system  to  system,  carrying  the  blood- 
vessels with  them.  Between  the  lamellae  are  branched  cells  which 
lie  in  cell-spaces,  or  cavities,  called  lacuna  (little  lakes),  and 
running  out  in  a  wheel-like  or  radial  direction  from  each  lacuna 
are  numerous  tiny  wavy  canals  called  canaliculi,  connecting  one 
lacuna  with  another,  and  forming  a  system  of  minute  channels 
which  communicate  with  each  other  and  with  the  Haversian  canal. 
This  constitutes  an  Haversian  System,  so  named  from  Havers,  a 
celebrated  anatomist.  Bone  is  composed  of  countless  such  sys- 
tems. The  spaces  between  these  systems  are  filled  by  lamellae 
arranged  at  irregular  angles. 

Marrow.  —  Marrow  consists  of  fibrous  tissue  with  blood-vessels, 
fat  cells,  marrow-cells,  and  red  corpuscles.  There  are  two  distinct 
kinds  of  marrow,  yellow  and  red.  Yellow  marrow  contains  a 


56  ANATOMY  AND   PHYSIOLOGY         [CHAP.  IV 

larger  per  cent  of  fat,  and  is  found  in  the  medullary  canals  of  the 
long  bones.  Red  marrow  contains  less  fat,  but  is  highly  vascular 
and  occupies  the  spaces  in  cancellous  bone.  The  function  of  mar- 
row is  (1)  to  support  the  blood-vessels,  lymphatics,  and  nerves; 
(2)  to  serve  as  a  source  of  nourishment  for  bone;  and  (3)  as  a 
location  for  the  formation  of  red  cells.  (See  page  157.) 

Periosteum.  —  All  bones  are  covered,  except  at  the  joints,  by  a 
vascular  fibrous  membrane,  the  periosteum  (around  the  bone) .  It 
consists  of  an  outer  fibrous  layer  and  an  inner  vascular  layer.  The 
attachment  of  the  periosteum  to  bone  is  rendered  firmer  by  inward 
prolongations  of  the  fibrous  layer  called  the  fibres  of  Sharpey. 

Blood-vessels.  —  Unlike  cartilage,  the  bones  are  plentifully 
supplied  with  blood.  If  we  strip  the  periosteum  from  a  fresh 
bone,  we  see  many  bleeding  points  representing  the  canals 
(Yolkman's)  through  which  the  blood-vessels  enter  and  leave  the 
bone.  These  blood-vessels  proceed  from  the  periosteum  to  join 
the  system  of  Haversian  canals.  Around  the  Haversian  canals 
the  lamellse  are  disposed,  while  lying  between  them,  arranged  in 
circles,  are  found  the  lacunae,  which  contain  the  bone-cells. 
Running  from  one  lacuna  to  another  in  a  radial  direction  through 
the  lamellse  towards  the  centre  are  the  canaliculi.  Following  this 
scheme,  it  will  be  seen  that  the  innermost  canaliculi  run  into  the 
Haversian  canals,  and  thus  is  established  a  direct  communication 
between  the  blood  in  these  canals  and  the  cells  in  the  lacunse  con- 
nected with  and  surrounding  each  Haversian  canal.  In  this  way 
the  whole  substance  of  the  bone  is  penetrated  by  intercommuni- 
cating channels,  and  the  nutrient  matters  and  mineral  salts  from 
the  blood  in  the  Haversian  canals  can  find  their  way  to  every  part. 

Function  of  periosteum  in  growth  of  bone.  —  In  the  embryo 
the  foundation  of  the  skeleton  is  laid  in  cartilage,  or  in  primitive 
connective  tissue,  ossification  of  the  bones  occurring  later.  The 
hardening  or  ossification  of  the  bones  is  accomplished  by  the 
penetration  of  blood-vessels  and  bone-cells,  called  osteoblasts, 
from  the  periosteum.  As  they  penetrate  into  the  cartilaginous 
or  membranous  models,  they  absorb  the  cartilage  and  connective 
tissue  and  deposit  the  true  bone  tissue  at  various  points  until  they 
form  the  particular  bony  structure  with  which  we  are  familiar. 

Regeneration  of  bone.  —  A  fracture  is  usually  accompanied 
by  injury  to  the  periosteum  and  tissues.  This  results  in  inflam- 


CHAP.  IV]  SUMMARY  57 

mation,  which  means  that  an  increased  amount  of  blood  is  sent  to 
the  part.  The  plasma  and  white  blood  corpuscles  from  the  blood 
exude  into  the  tissues  and  form  a  viscid  substance,  which  sticks  the 
ends  of  the  bone  together,  and  is  called  callus.  Usually  bone-cells 
from  the  periosteum  and  lime  salts  are  gradually  deposited  in  the 
callus,  which  eventually  becomes  hardened  and  forms  new  bone. 
Occasionally  the  callus  does  not  ossify  and  a  condition  known  as 
fibrous  union  results.  The  periosteum  is  largely  concerned  in  this 
process  of  repair ;  for  if  a  portion  of  the  periosteum  be  stripped  off. 
the  subjacent  bone  will  be  liable  to  die,  while  if  a  large  part  or  the 
whole  of  a  bone  be  removed,  and  the  periosteum  at  the  same  time 
left  intact,  the  bone  will  wholly  or  in  a  great  measure  be  regen- 
erated. 

SUMMARY 

CONNECTIVE  TISSUE  —  A  tissue  of  cells  with  a  great  deal  of  inter- 
cellular substance,  which  is  derived  from  the  cells. 

1.  Resemble  each  other  in  function. 
Reasons  for  classification  {  2.  Resemble  each  other  in  origin.1 

3.  Resemble  each  other  in  structure. 
Areolar,         Reticular, 
Fibrous,        Neuroglia, 
Elastic,          Cartilage, 
Adipose,        Bone. 
Areolar  tissue.  —  Formed  by  interlacing  of  wavy  bundles  of  white  fibres 

and  some  straight  elastic  fibres  with  cells  lying  in  the  spaces. 
Fibrous  tissue.  —  Formed  of  wavy  bundles  of  white  fibres  only,  with  cells 

in  rows  between  bundles.     Very  strong  and  tough  but  pliant. 
Elastic  tissue.  —  Formed  of  yellow  elastic  fibres  with  few  bundles  of  white 
fibres.     It  is  extensile  and  elastic. 

Areolar  tissue  connects,  insulates,  forms  protecting  sheaths, 

and  is  continuous  throughout  the  whole  body. 
Fibrous  tissue  is  found  in  form  of  ligaments,  tendons,  apo- 


Classification 


Function 


neuroses,  protecting  sheaths,  and  fasciae. 


Elastic  tissue  serves  same  purpose  as  India  rubber.     Saves 
wear  and  tear  of  muscles.     Found  in  ligamenta  flava,  blood- 
vessels, air-tubes,  vocal  cords,  lungs,  and  larynx. 
Adipose  tissue.  —  Modification  of  areolar  tissue,  with  cells  enlarged  and 
filled  with  fat.     Distribution  quite  general  but  not  uniform. 

1.  Forms  a  reserve  fund  for  the  production  of  energy. 
Function  <|  2.  Prevents  the  too  rapid  loss  of  heat. 

3.  Serves  to  protect  and  support  delicate  organs. 

1  With  one  exception,  neuroglia. 


58 


ANATOMY  AND   PHYSIOLOGY         [CHAP.  IV 


Varieties 


Reticular  tissue.  —  Network  of  white  fibres  with  few  yellow  fibres.  Cells 
wrapped  around  fibres. 

Lymphoid  tissue.  —  Reticular  tissue'  with  meshes  of  network  occupied 
by  lymph  corpuscles. 

Function.  —  Reticular  tissue  forms  a  fine  framework  in  many  organs, 
e.g.,  muscles.  —  Lymphoid  tissue  forms  the  structure  of  the  spleen  and 
lymph-nodes.  Also  enters  into  composition  of  glands  and  mucous 
membranes. 

Neuroglia.  —  Consists  of  cells  that  give  off  processes  which  form  a  net- 
work. 

Function.  —  Forms  a  supporting  framework  for  nerve  tissue. 

Cartilage. : —  Cartilage  or  gristle  is  a  bluish  white  tissue,  firm  and  elastic, 
covered  and  nourished  by  perichondrium. 

[  Articular  1  „ 

1.  Hyaline  cartilage  |  Cogtal      j  Skeletal. 

2.  White  fibro-cartilage. 

3.  Yellow  fibro-cartilage. 

Hyaline  —  Small  number  of  cells  in  an  abundant  quantity  of  intercellular 
substance.  Found  as  articular  cartilage,  covering  ends  of  bones  in 
joints.  Found  as  costal  cartilage,  connecting  ribs  and  sternum,  or  one 
rib  with  another. 

White  Fibro  —  Intercellular  substance  pervaded  with  white  fibres.     Re- 
sembles fibrous  tissue.     Found  between  spinal  and  pubic  bones. 
Yellow  Fibro  —  Intercellular  substance  pervaded  with  network  of  yellow 
elastic  fibres.     Found  in  parts  of  throat  and  ear. 

Serves  as  cushions  for  ends  of  bones. 
Makes  a  flexible   connection  between 
the  ribs  and  the    sternum,  or  be- 
tween     one      rib      and     another. 
Strengthens   and    maintains   shape 
of  certain  organs  without  rigidity. 
Serves  as  strong,   flexible,  connecting 
material  between  bones. 

f  Strengthens  and  maintains    shape  of 
certain  organs,   and    yet  allows  of 
certain  amount  of  elasticity. 
Bone,  or  osseous,  tissue.  —  Bone  is  connective  tissue  in  which  the  inter- 
cellular substance  derived  from  the  cells  is  rendered  hard  by  being  im- 
pregnated with  mineral  salts. 

(  Calcium  phosphate. 
Mineral  matter  |  Calcium  carbonate. 

[  Small  portion  of  other  salts. 
f  Blood-vessels. 

Organic  matter  <  Connective  tissue. 
I  Marrow, 


Function 


Hyaline  cartilage 


White  fibro-cartilage 


Composition 


CHAP.  IV] 


SUMMARY 


59 


Varieties 


Canals 


Haversian 
system 


Haversian 


I  Cancellated  or  spongy. 
I  Dense  or  compact  like  ivory. 
Medullary  —  Yellow  marrow. 
f  Blood-vessels. 
1  Lymphatics. 
Haversian   canals,   branch   freely   and   connect 

system  to  system. 
Lamella?  —  bony  fibres  arranged  in  rings  around 

Haversian  canals. 

Lacunae  —  small    spaces    between    lamellae    oc- 
cupied by  bone-cells. 
Canaliculi  —  canals  which  radiate  from  lacunae 

to  the  Haversian  canals. 
Endosteum  —  A  fibrous  membrane  that  lines  the  medullary  canal. 
Consists  of  !  Fibrous  tissue,  blood-vessels,  fat  cells,  mar- 
l     row  cells,  and  red  corpuscles. 
Yellow  —  found    in    medullary    canals    of 

long  bones. 
Red  —  occupies  spaces  in  cancellous  bone. 

1.  Supports  blood-vessels,  lymphatics,  and 
nerves. 

2.  Serves  as   a  source  of  nourishment  for 
bone. 

3.  Serves  as  location  for  formation  of  red 
corpuscles. 

Periosteum  —  A  vascular  fibrous  membrane  that  covers  the  bones 
and  serves  to  nourish  them.  Important  in  reunion  of  broken  bone 
and  growth  of  new  bone. 

Fibres  of  Sharpey  —  Inward  prolongations  of  periosteum. 


Marrow 


Varieties 


Function 


CHAPTER  V 

THE  SKELETON.  —  CLASSIFICATION  OF  BONES;  DIVISIONS  OF 
THE  SKELETON;  BONES  OF  THE  CRANIUM;  BONES  OF  THE 
FACE;  BONES  OF  THE  TRUNK;  BONES  OF  THE  UPPER  EX- 
TREMITIES;  BONES  OF  THE  LOWER  EXTREMITIES 

Function.  —  The  bones  are  the  principal  organs  of  support,  and 
the  passive  instruments  of  locomotion.  Connected  together  in  the 
skeleton,  they  form  a  framework  of  hard  material,  affording  at- 
tachment to  the  soft  parts,  maintaining  them  in  their  due  posi- 
tion, sheltering  such  as  are  of  delicate  structure,  giving  stability 
to  the  whole  fabric,  and  preserving  its  shape. 

The  entire  skeleton  in  the  adult  consists  of  two  hundred  and  six 
named  bones.  These  are  :  — 

Cranium 8] 

Face 14 

f  Malleus  2  1 
Ear  |  Incus  2      > 6 

I  Stapes  2    J 

Hyoid I  \  206 

The  spine,  or  vertebral  column 

(sacrum  and  coccyx  included)  26 

Sternum  and  ribs 25 

Upper  extremities 64 

Lower  extremities 62 

In  this  enumeration  the  sesamoid 1  bones,  which  are  found  em- 
bedded in  tendons  covering  the  bones  of  the  knee,  hand,  and  foot, 
are  not  included. 

CLASSIFICATION 

The  bones  may  be  divided,  according  to  their  shape,  into  four 
classes:  1.  Long,  2.  Short,  3.  Flat,  and  4.  Irregular. 

Long  bones.  —  A  long  bone  consists  of  a  shaft  and  two  extrem- 
ities. The  shaft  is  formed  mainly  of  compact  tissue,  this  compact 

1  Ses'amoid  [from  the  Greek  sesamon,  a  "seed  of  the  sesamum,"  and  eidos,  "  form," 
"resemblance  "],  resembling  a  grain  of  sesamum. 

60 


CHAP.  V] 


THE   SKELETON 


61 


tissue  being  thickest  in  the  middle,  where  the  bone  is  most  slender 
and  the  strain  greatest,  and  it  is  hollowed  out  in  the  interior  to 
form  the  medullary  canal.  (See  Fig.  27.)  The  extremities  are 
made  up  of  cancellated  tissue  with  only  a  thin  coating  of  compact 


-PARIETAL 
-TEMPORAL 


CARPUS 
METACARPUS 


FIG.  30.  —  THE  HUMAN  SKELETON.     (Morrow.) 

substance,  and  are  more  or  less  expanded  for  greater  convenience 
of  mutual  connection,  and  to  afford  a  broad  surface  for  muscular 
attachment.  All  long  bones  are  more  or  less  curved,  which  gives 
them  greater  strength.  The  long  bones  are  as  follows :  — 


62  ANATOMY  AND   PHYSIOLOGY          [CHAP.  V 

2  Clavicle  2  Tibia 

2  Humerus  2  Fibula 

2  Radius  10  Metacarpals 

2  Ulria  10  Metatarsals 

2  Femur  56  Phalanges 

Short  bones.  —  The  short  bones  are  small  pieces  of  bone  ir- 
regularly shaped.  Their  texture  is  spongy  throughout,  excepting 
at  their  surface,  where  there  is  a  thin  crust  of  compact  substance. 
The  short  bones  are  the  sixteen  bones  of  the  carpus,  the  fourteen 
bones  of  the  tarsus,  and  the  two  patellae. 

Flat  bones.  —  Where  the  principal  requirement  is  either  exten- 
sive protection  or  the  provision  of  broad  surfaces  for  muscular 
attachment,  the  bony  tissue  expands  into  broad  or  elongated 
flat  plates  which  are  composed  of  two  thin  layers  of  compact 
tissue,  enclosing  between  them  a  variable  quantity  of  cancellous 
tissue.  The  flat  bones  are  as  follows :  - 

1  Occipital  2  Lacrimal 

2  Parietal  2  Scapula 

1  Frontal  1  Sternum 

2  Nasal  24  Ribs 

1  Vomer  2  Hip  bones 

Irregular  bones.  —  The  irregular  bones  are  those  which,  on 
account  of  their  peculiar  shape,  cannot  be  grouped  under  either 
of  the  preceding  heads.  The  irregular  bones  are  as  follows  :  - 

24  Vertebrae  2  Malar 

1  Sacrum  2  Maxillae 

1  Coccyx  1  Mandible 

2  Temporal  2  Palate 

1  Sphenoid  2  Inferior  turbinated 

1  Ethmoid  1  Hyoid 

The  bones  of  the  ear  are  so  small  that  they  are  described  as  ossicles 
and  do  not  fit  in  any  of  these  groups. 

Processes  and  depressions.  —  If  the  surface  of  any  bone  is 
examined,  certain  projections  and  depressions  are  seen.  The  pro- 
jections are  called  processes.  The  depressions  are  called  fosses 
or  cavities ,  and  either  a  qualifying  adjective  is  used  to  describe 
them,  or  a  special  name  given  to  them.  Processes  and  depressions 
are  classified  as  :  1.  Articular,  2.  Non-articular.  The  articular  are 
provided  for  the  mutual  connection  of  bones  to  form  joints.  The 


CHAP.  V]  THE   SKELETON  63 

non-articular  serve  for  the  attachment  of  ligaments  and  muscles. 
The  following  terms  are  used  :  — 

Process.  —  Any  marked  bony  prominence. 

Tuberosity.  —  A  large  process. 

Tubercle.  —  A  small  process. 

Spinous.  —  A  sharp,  slender  process. 

Crest.  —  A  narrow  ridge  of  bone. 

Condyle.  —  A  rounded  or  knuckle-like  process. 

Head.  —  A  portion  supported  on  a  constricted  part  or  neck. 

Fossa.  —  A  depression  in  or  upon  a  bone. 

Cavities.  —  The  terms  sinus  l  and  antrum  are  applied  to  cavities 
within  certain  bones. 

Meatus  or  Canal.  —  A  long  tube-like  passageway. 

Fissure.  —  A  narrow  slit. 

Foramen.  —  A  hole  or  orifice  through  which  blood-vessels,  nerves, 
and  ligaments  are  transmitted. 

DIVISIONS  OF  THE   SKELETON 

In  taking  up  the  various  divisions  of  the  skeleton,  we  will  con- 
sider it  as  consisting  of  — 

f  Cranium. 

1.  Head  or  skull     ....     {  -, 

1  Face. 

2.  Hyoid. 

Vertebrae. 


3.  Trunk 


Sternum. 


fc  Ribs. 

4.  Upper  extremities. 

5.  Lower  extremities. 

The  head  or  skull.  —  The  head  or  skull  rests  upon  the  spinal 
column,  and  is  formed  by  the  union  of  the  cranial  and  facial 
bones.  It  is  divisible  into  —  1.  Cranium,  or  brain  case,  and 
2.  Anterior  region,  or  face. 

BONES   OF  THE   CRANIUM 

Occipital 1 

Parietal 2 

Frontal 1 

Temporal       2 

Ethmoid 1 

Sphenoid       1 

1  The  term  "sinus"  is  also  used  in  surgery  to  denote  a  narrow  tract  leading  from 
the  surface  down  to  a  cavity. 


8 


64 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  V 


Occipital  bone.  —  It  is  situated  at  the  back  and  base  of  the 
skull.     At  birth  the  bone  consists  of  four  parts,  which  do  not 


FRONTAL 


WINGOFSPHENOID 

NASAL 

LACRIMAL 

MALAR 

MAXILLA 


MANDIBLE 


PARIETAL 

TEMPORAL 

OCCIPITAL 
MASTOID  PROCESS 


FIG.  31.  —  SIDE  VIEW  OP  THE  SKULL. 


unite  into  a  single  bone  until  the  sixth  year.  The  internal  sur- 
face is  deeply  concave,  and  presents  many  eminences  and  depres- 
sions for  the  reception  of  parts  of  the  brain.  There  is  a  large 


FRONTAL-* 


LEFT  PARIETAL 


INFERIOR 
TU  RBI  NATE 


MANDIBLE 


FIG.  32.  —  FRONT  VIKW  OK  THE  SKULL. 


CHAP.  V]  THE  SKELETON  65 

hole  —  the  foramen  magnum  —  in  the  inferior  portion  of  the  bone, 
for  the  transmission  of  the  medulla  oblongata  (the  constricted 
portion  of  the  brain)  where  it  narrows  down  to  join  the  spinal 


Cerebral 
Fossa 


FIG.  33.  —  OCCIPITAL,  BONE.     Inner  surface. 

cord.  At  the  sides  of  the  foramen  magnum  it  presents  two 
processes  called  condyles,  which  articulate  with  the  first  vertebra. 

Parietal  bones.  —  The  right  and  left  form  by  their  union  the 
greater  part  of  the  sides  and  roof  of  the  skull.  The  external  sur- 
face is  convex  and  smooth ;  the  internal  surface  is  concave,  and 
presents  eminences  and  depressions  for  lodging  the  convolutions  of 
the  brain,  and  numerous  furrows  for  the  ramifications  of  arteries 
which  supply  the  dura  mater  (membrane  which  covers  the  brain) 
with  blood. 

Frontal  bone.  —  It  resembles  a  cockle  shell,  and  not  only  forms 
the  forehead,  but  also  enters  into  the  formation  of  the  roof  of  the 
orbits,  and  of  the  nasal  cavity.  The  arch  formed  by  part  of  the 
frontal  bone  over  the  eye  is  sharp  and  prominent,  and  is  known  as 
the  supraorbital  margin.  Just  above  the  supraorbital  margins  are 
hollow  spaces  called  the  frontal  sinuses  (see  Fig.  40)  which  are 
F 


66 


ANATOMY  AND  PHYSIOLOGY          [CHAP.  V 


filled  with  air  and  open  into  the  nose.  In  the  upper  and  outer 
angle  of  each  orbit  are  two  depressions  called  lacrimal  fossae  for 
the  reception  of  the  glands  of  the  same  name,  which  secrete  the 
tears.  At  birth  the  bone  consists  of  two  pieces,  which  afterwards 
become  united  along  the  middle  line,  by  a  suture  *  which  runs  from 


Supraorbital 

Margin 

Roof  of 
Orbital  Cavity 


Frontal  Sinuses 
FIG.  34.  —  FRONTAL  BONE. 

the  vertex  of  the  bone  to  the  root  of  the  nose.  This  suture  usually 
becomes  obliterated  within  a  few  years  after  birth,  but  it  occasion- 
ally remains  throughout  life. 

Temporal  bones.  —  The  right  and  left  are  situated  at  the  sides 
and  base  of  the  skull.  They  are  named  temporal  from  the  Latin 
word  tempus,  time,  as  it  is  on  the  temples  the  hair  first  becomes 
gray  and  thin,  and  thus  shows  the  ravages  of  time.  The  temporal 
bones  are  divided  into  three  parts  —  the  hard,  dense  portion, 
called  petrous;  a  thin  and  expanded  scale-like  portion,  called 
squamous;  and  a  mastoid  portion,  which  is  prolonged  down- 
ward and  forms  the  mastoid  process.  This  process  is  filled  with 
a  number  of  connected  cancellous  spaces,  containing  air,  and 
called  mastoid  cells.2  They  communicate  with  the  cavity  of  the 
middle  ear.  The  condition  known  as  mastoiditis  means  inflam- 
mation of  the  lining  of  these  cells. 

The  internal  ear,  the  essential  part  of  the  organ  of  hearing, 
is  contained  in  a  series  of  cavities,  channelled  out  of  the  substance 

1  See  Figs.  66  and  67. 

2  Cells.  —  The  student  must  bear  in  mind  that  the  word  cell  is  used  with  two 
different  meanings  in  anatomy.     Histologically  speaking,  the  word  "cell"  refers  to 
one  of  the  component  units  of  the  body,  such  as  an  "epithelial  cell  "  or  "nerve  cell." 

In  connection  with  the  use  of  the  words  "mastoid  cells"  in  the  text,  the 
word  "cells"  refers  to  tiny  enclosed  hollow  chambers. 


CHAP.  V] 


Till]   SKELETON 


67 


of  the  petrous  portion.  Between  the  squamous  and  petrous  por- 
tions is  a  socket,  called  the  glenoid  fossa,  for  the  reception  of  the 
condyle  of  the  lower  jaw. 


FIG.  35.  —  THE  RIGHT  TEMPORAL  BONE.    Outer  surface.    The  dotted  lines  indicate 
the  lines  of  suture  between  squamous,  mastoid,  and  petrous  portions.     (Gerrish.) 

Ethmoid  bone.  —  It  is  an  exceedingly  light  cancellous  bone 
that  forms  part  of  the  orbits,  nasal  fossae,  and  base  of  the  cranium. 
It  consists  of  a  horizontal  plate,  a  vertical  plate  (see  Fig.  36),  and 


HORIZONTAL  PLATE 
SHOWING  FORAM/NA 


VERTICAL  PLATE 


LATERAL 
MASS 


FIG.  36.  —  ETHMOID  BONE.     Seen  from  under  surface. 

two  lateral  masses.     The  horizontal  plate  forms  the  roof  of  the 
nasal  fossae,  and  also  closes  the  anterior  part  of  the  base  of  the 


68 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  V 


cranium.  It  is  pierced  by  numerous  foramina  or  holes,  'through 
which  the  nerves  conveying  the  sense  of  smell  pass.  Descending 
from  the  horizontal  plate  is  the  vertical  plate  which  helps  to  form 
the  nasal  septum,  and  on  either  side  the  lateral  masses  help  to  form 
the  side  walls  of  the  nasal  fossae.  The  lateral  masses  contain  a 
number  of  thin-walled  cavities  called  the  ethmoidal  sinuses,  which 

communicate  with  the 
nasal  fossae.  Descend- 
ing from  the  horizontal 
plate  on  either  side  of 
the  septum  are  two 
processes  of  very  thin, 
cancellous,  bony  tissue, 
named  the  superior  and 
middle  turbinated  pro- 
cesses. (See  Fig.  153.) 
Sphenoid  bone.  —  It 
is  situated  at  the  an- 
terior part  of  the  base 
of  the  skull  and  binds 
the  other  cranial  bones 
together.  It  helps  to 
form  the  cavities  of  the 
cranium,  orbits,  and 
nasal  fossae.  In  form 
it  somewhat  resembles 
a  bat  with  extended  wings,  and  is  described  as  consisting  of  a 
body,  two  pairs  of  wings,  and  two  pterygoid  processes.  The 
body  is  joined  to  the  ethmoid  in  front  and  the  occipital  behind. 
It  contains  cavities  which  are  called  sphenoidal  sinuses.  (See 
Fig.  40.)  They  communicate  with  the  nasal  fossae. 

THE  SKULL  AS  A  WHOLE 

The  cranium  is  a  firm  case  or  covering  for  the  brain.  Four  of 
the  eight  bones  which  form  this  bony  covering  are  classed  as  flat 
bones.  They  consist  of  two  layers  of  compact  tissue,  the  outer 
one  thick  and  tough,  the  inner  one  thinner  and  more  brittle.  The 
cancellated  tissue  lying  between  these  two  layers,  or  "  tables  of  the 
skull,"  is  called  the  diploe.  The  base  of  the  skull  is  much  thicker 


FIG.  37.  —  PARIETAL,  TEMPORAL,  AND  SPHENOID 
BONES.  Posterior  aspect.  1,  body  of  sphenoid 
bone;  2,  2,  greater  wings  of  sphenoid  bone;  3,  3, 
parietal  bones ;  4,  4,  mastoid  process  of  temporal 
bones ;  5,  5,  external  pterygoid  plate  ;  6,  6,  internal 
pterygoid  plate.  (Gould's  Dictionary.) 


CHAP.  V] 


THE  SKELETON 


69 


>. 


and  stronger  than  the  walls  and  roof;    it  presents  a  number  of 
openings  for  the  passage  of  the  cranial  nerves,  blood-vessels,  etc. 

The  bones  of  the  cranium  begin  to  develop  at  a  very  early 
period  of  foetal  life.  Thus,  before  birth  the  bones  at  the  top  and 
sides  of  the  skull  are  separated 
from  each  other  by  membranous 
tissue  in  which  bone  is  not  yet 
formed,  and  being  then  imper- 
fectly ossified,  they  are  readily 
moulded,  and  overlap  one  an- 
other more  or  less  during  par- 
turition. The  spaces  at  the 
angles  of  the  bone  occupied  by 
the  membranous  tissue  are 
termed  the  fontanelles,  so  named 
from  the  pulsations  of  the  brain,  FlG-  J8-  -7  SKULL  ?*  NEW-*°fN  CHILD. 

To  show  moulding.     (Edgar.) 

which  can  be  seen  in  some  of 

them  and  which  the  early  anatomists  likened  to  the  rise  and 

fall  of  water  in  a  fountain.     There  are  six  of  these  fontanelles. 
Anterior  fontanelle.  —  The  anterior  fontanelle  is  the  largest, 

and  is  a  lozenge-shaped  space  between  the  angles  of  the  two 

parietal  bones  and  the  two  seg- 
ments of  the  frontal  bone.  It 
remains  open  until  the  second 
year,  and  occasionally  persists 
throughout  life.  (See  Fig.  66.) 

Posterior  fontanelle.  -  -  The 
posterior  fontanelle  is  much 
smaller  in  size,  and  is  a  triangu- 
lar space  between  the  occipital 
and  two  parietal  bones.  This  is 
closed  by  an  extension  of  the 

FIG.  39.  — SKULL  OF  NEW-BORN  CHILD.     Ossifying   process    a    few    months 


To  show  moulding.     (Edgar.) 


after  birth.     (See  Fig.  67.) 


The  other  four  fontanelles,  two  on  each  side  of  the  skull,  are 
placed  at  the  inferior  angles  of  the  parietal  bones;  they  are  un- 
important. Small,  irregular  ossicles  called  sutural  bones  (Wor- 
mian  bones)  are  found  in  the  sutures  of  the  head,  chiefly  near  the 
fontanelles,  and  often  assist  in  the  closure  of  the  fontanelles. 


70 


ANATOMY   AND   PHYSIOLOGY         [CHAP.  V 


Sinuses  of  the  head.  —  Four  sinuses  communicate  with  each 
nasal  cavity  :  the  frontal,  ethmoidal,  sphenoidal,  and  maxillary  or 
antrum  of  Highmore.  The  mucous  membrane  which  lines  the  nose 
also  lines  all  of  these  sinuses,  and  inflammation  of  this  membrane 
may  extend  into  any  of  them  and  cause  sinusitis.  (See  Fig.  97.) 


BONES  OF  THE   FACE 

Nasal 2 

Vomer 1 

Inf.  Turbinated 2 

Lacrimal 2 

Malar 2 

Palate 2 

Maxillae 2 

Mandible    .  1 


14 


Nasal  bones.  —  They  are  two  small  oblong  bones  placed  side 
by  side  at  the  middle  and  upper  part  of  the  face,  forming  by  their 
junction  "  the  bridge  "  of  the  nose.  (See  Fig.  31.) 

Vomer.  —  It  is  a  single  bone  placed  at  the  lower  and  back  part 
of  the  nasal  cavity,  and  forms  part  of  the  central  septum  of  the 


ANTERIOR    PALA 
T.NE    GROOVE 


HARD    PALATE 


FIG.  40.  —  SAGITTAL  SECTION  OF  FACE,  A  LITTLE  TO  THE  LEFT  OF  THE  MIDDLE 
LINE,  SHOWING  THE  VOMEK  AND  ITS  RELATIONS.     (Gerrish.) 

nasal  fossse.  It  is  thin,  and  shaped  somewhat  like  a  ploughshare, 
but  varies  in  different  individuals,  being  frequently  bent  to  one 
or  the  other  side,  thus  making  the  nasal  chambers  of  unequal  size. 


CHAP.  V] 


THE  SKELETON 


71 


FIG.  41.— 
LACRIMAL 
BONE. 


Inferior  turbinated  bones.  —  They  are  situated  in  the  nostril, 
on  the  outer  wall  of  each  side.  Each  consists  of  a  layer  of  thin, 
cancellous  bone,  curled  upon  itself  like  a  scroll;  hence  its  name, 
"  turbinated."  They  are  below  the  superior  and  middle  turbi- 
nated processes  of  the  ethmoid  bone.  Abnormal  con- 
ditions of  these  bones  and  the  membranes  covering 
them  cause  some  of  the  more  common  nasal  diseases. 
(See  Fig.  153.) 

Lacrimal  bones.  —  Are  the  smallest  and  most  fragile 
bones  of  the  face.  They  are  situated  at  the  front 
part  of  the  inner  wall  of  the  orbit,  and  somewhat 
resemble  a  finger-nail  in  form,  thinness,  and  size. 
They  are  named  lacrimal  because  they  contain  part 
of  the  canal  through  which  the  tear  duct  runs. 

Malar,  or  yoke  bone.  —  Forms  the  prominence  of  the  cheek, 
and  part  of  the  outer  wall  and  floor  of  the  orbit.  (See  Figs.  31  and 
32.)  A  prominent  spine  of  bone  projects  backward  from  the  body 
of  the  malar,  and  articulates  by  its  free  extremity  with  the  cor- 
responding spine  projecting  forward  from  the  temporal  bone,  thus 

making  the  two  mem- 
bers of  the  true  arch 
known  as  the  zygomatic 
arch.  (See  Fig.  35.) 

Palate  bones. — They 
are  shaped  like  an  "  L," 
and  form  (1)  the  back 
part  of  the  roof  of  the 
mouth  ;  (2)  part  of  the 
floor  and  outer  wall  of 
the  nasal  fossa? ;  (3)  a 
very  small  portion  of 
the  floor  of  the  orbit. 

Maxillae,  or  upper 
jaw-bones,  also  known 
as  superior  maxillary.  —  The  maxillae  are  two  in  number  (right  and 
left)  and  are  the  principal  bones  of  the  face.  Before  birth  these 
bones  usually  unite  to  form  one  bone.  When  they  fail  to  do  so  we 
have  the  condition  known  as  deft  palate.  Each  bone  assists  in  form- 
ing (1)  part  of  the  floor  of  the  orbit,  (2)  the  floor  and  outer  wall 


RiOSlTY 
PTERYGOID   FOSSA 


FIG.  42.  —  THE  Two  PALATE  BONES  IN  THEIR 
NATURAL  POSITION.     Dorsal  view.     (Gerrisb.) 


72 


ANATOMY  AND  PHYSIOLOGY          [CHAP.  V 


NASAL 
PROCESS 


FIG.  43.  — THE  RIGHT  MAXILLA. 
Outer  surface.     (Gerrish.) 


of  the  nasal  fossae,  (3)  the  greater 
part  of  the  roof  of  the  mouth. 

That  part  of  the  bone  which 
contains  the  teeth  is  called  the  al- 
veolar process,  and  is  excavated 
into  cavities,  varying  in  depth  and 
size  according  to  the  size  of  the 
teeth  they  contain.  The  body  of 
the  bone  is  hollowed  out  into  a 
large  cavity  known  as  the  antrum 
of  Highmore,  which  opens  into  the 
nose.  Abnormal  conditions  of 
either  the  nose  or  teeth  may  cause 
an  infection  of  these  an tr urns. 

Mandible,  or  lower  jaw-bone,  also  known  as  inferior  maxillary. 
—  It  is  the  largest  and  strongest  bone  of  the  face.  At  birth,  it 
consists  of  two  lat- 
eral halves,  which 
join  and  form  one 
bone  during  the  first 
or  second  year.  It 
serves  for  the  recep- 
tion of  the  lower 
teeth,  and  undergoes 
several  changes  in 
shape  during  life, 
owing  mainly  (1)  to 
the  first  and  second 
dentition,  (2)  to  the 
loss  of  teeth  in  the  aged,  and  (3)  the  subsequent  absorption  of 
that  part  of  the  bone  which  contained  them.  It  articulates, 

by  its  condyles,  with  the 
sockets  in  the  temporal 
bones,  which  allows  for 
free  movement  in  mastica- 
tion. 

Hyoid   bone   (os  hyoid- 

m 

FIG.  45. -THE  HYOID  BONE.     Viewed  from      eum)«  ~  '  ^       an       isolated 
the  left  and  in  front.     (Gerrish.)  U-shaped      bone     lying     in 


FIG.  44.  —  THE  MANDIBLE.     Viewed  from  the  right 
and  a  little  in  front.      (Gerrish.) 


CHAP.  V] 


THE  SKELETON 


73 


front  of  the  throat,  just  above  the  laryngeal  prominence  (Adam's 
apple) .  It  supports  the  tongue,  and  gives  attachment  to  some  of 
its  numerous  muscles. 

TRUNK 

The   bones   which   enter    into    the    formation    of    the   trunk 
consist  of  the  vertebrae,  sternum,  and  ribs. 


FIG.  46.  —  THE  VERTEBRAL  COLUMN.     Right  lateral  view  and  dorsal  view. 

(Gerrish.) 

i 

The  vertebral  column  as  a  whole.  —  It  is  formed  of  a  series  of 
bones  called  vertebrae,  and  in  a  man  of  average  height  is  about 
twenty-eight  inches  long.  In  youth  the  vertebrae  are  thirty- 


74 


ANATOMY  AND  PHYSIOLOGY          [CHAP.  V 


three  in  number,  and  according  to  the  position  they  occupy  are 
named :  — 


Cervical,  in  the  neck       7 

Thoracic,  in  the  thorax 12 

Lumbar,  in  the  loins 5 

Sacral,  in  the  pelvis 5 

Coccygeal,  in  the  pelvis       ....  4 


True  vertebrae. 


False  vertebrae. 


Spinons  Troccss 


FIG.  47.  —  A  CERVICAL  VERTEBRA. 


The  vertebrae  in  the  three  upper  portions  of  the  spine  are 
separate  and  movable  throughout  the  whole  of  life,  and  are  known 

as  true  vertebrae. 
Those  found  in  the 
sacral  and  coccygeal 
regions  are,  in  the 
adult,  firmly  united, 
so  as  to  form  two 
bones,  five  entering 
into  the  upper  bone, 
or  sacrum,  and  four 
into  the  terminal 
bone  of  the  spine,  or 
coccyx.  They  are 
known  as  false  ver- 
tebrae, and  on  account  of  their  union  the  number  of  vertebrae 
in  the  adult  is  twenty-six. 

The  vertebrae.  —  Each  vertebra  consists  of  two  essential 
parts,  an  anterior  solid  portion  or  body,  and  a  posterior  portion  or 
arch.  Each  arch  has  seven  processes  :  four  articular,  two  to  con- 
nect with  bone  above,  two  to  connect  with  bone  below ;  two  trans- 
verse, one  at  each  side,  and  one  spinous  process,  projecting  back- 
ward. 

Cervical  vertebra.  —  In  the  cervical  region  of  the  vertebral  col- 
umn the  bodies  of  the  vertebrae  are  smaller  than  in  the  thoracic, 
but  the  arches  are  larger.  The  spinous  processes  are  short,  and 
are  often  cleft  in  two,  or  bifid.  The  transverse  processes  are 
pierced  by  a  foramen  for  the  passage  of  blood-vessels  and  nerves. 
The  first  and  second  cervical  vertebrae  differ  considerably  from 
the  rest.  The  first,  or  atlas,  so  named  from  supporting  the  head 
has  practically  no  body,  and  may  be  described  as  a  bony  ring 
divided  into  two  sections  by  a  transverse  ligament.  The  dorsal 


CHAP.  V]  THE  SKELETON  75 

section  of  this  ring  contains  the  spinal  cord,  and  the  ventral  or 
front  section  contains  the  bony  projection  which  arises  from  the 
upper  surface  of  the  body  of  the  second  cervical  vertebra,  the  axis 
(epistropheus) .  This  bony  projection,  called  the  odontoid  process, 
forms  a  pivot,  and  around  this  pivot  the  atlas  rotates  when  the 


COSTO-TRANS 
VERSE    FORAMEN 


TRANSVERSE 
PROCESS. 


DORSAL    SECTION 


FIG.  48.  —  THE  ATLAS.     Viewed  from  above.     (Gerrish.) 

head  is  turned  from  side  to  side,  carrying  the  skull,  to  which  it  is 
firmly  articulated,  with  it. 

Thoracic  vertebra.  —  The  bodies  of  the  thoracic  vertebrae  are 
larger  and  stronger  than  those  of  the  cervical  ;  and  have  a  facet 
or  demi-facet  for  articulation  with  the  vertebral  end  of  a  rib. 

Lumbar  vertebra  .  — 

The    bodies    of    the  .  ODO««ID  p.octss. 

lumbar  vertebra,  are 
the  largest  and 
heaviest  in  the  whole 


Structure    of   ver-  "" 


6PINOUS    PROCESS. 

T 

PROCESS. 

tebral  Column.  —  The  FIG.  49.  —  THE  Axis  (EPISTROPHEUS). 

•     j.  f     ^  Its  right  side.     (Gerrish.) 

bodies  or  the  ver- 
tebrae are  piled  one  upon  another,  forming  a  strong,  solid  pillar,  for 
the  support  of  the  cranium  and  trunk,  the  arches  forming  a  hollow 
cylinder  behind  for  the  protection  of  the  spinal  cord.  Viewed 
from  the  side,  it  presents  four  curves  which  are  alternately  convex 
and  concave.  The  two  concave  ones  are  called  primary  curves 
because  they  exist  in  foetal  life  and  are  designed  for  the  accom- 
modation of  viscera.  The  other  two  are  called  secondary  or 
compensatory  curves  because  they  enable  the  child  to  assume  the 
erect  attitude. 


76  ANATOMY  AND   PHYSIOLOGY          [CHAP.  V 

The  different  vertebrae  are  connected  (1)  by  means  of  the 
articular  processes,  (2)  by  disks  of  intervertebral  fibro-cartilage 
placed  between  the  vertebral  bodies,  and  (3)  by  broad  thin  liga- 
ments called  the  ligamenta  flava  which  connect  the  transverse 
processes.  The  spinal  curves  confer  a  considerable  amount  of 


TRUE   RIBS 


FALSE    RIBS 


FLOATING   RIBS 


FIG.  50.  —  THORAX. 


springiness  and  strength  upon  the  spinal  column,  which  would 
be  lacking  were  it  straight,  and  the  elasticity  is  further  increased 
by  the  ligamenta  flava,  and  the  discs  of  fibro-cartilage.  These 
discs  or  pads  also  mitigate  the  effects  of  concussion  arising  from 
falls  or  blows,  and  allow  of  a  certain  amount  of  motion  between 


CHAP.  V] 


THE  SKELETON 


77 


the  vertebrae.     The  amount  of  motion  permitted  is  greatest  in 
the  cervical  region. 

Abnormal  conditions.  —  As  a  result  of  injury  or  disease  the 
normal  curves  may  become  exaggerated  and  are  then  spoken  of 
as  curvatures.  Curvatures  may  be  lateral,  dorsal,  or  ventral. 

It  occasionally  happens  that  the  arch  of  one  of  the  vertebras 
does  not  develop  properly,  and  as  a  result  the  membranes  and 
fluid  of  the  spinal  cord  will  protrude,  forming  a  tumor  upon  the 
child's  back.  This  condition  is  called  spina  bifida. 

Sacrum  (os  sacrum) .  —  The  sacrum  is  formed  by  the  union 
of  the  five  sacral  vertebrae.  It  is  a  large  triangular  bone  situated 
like  a  wedge  between  the  coxal  bones,  and  is  curved  upon  itself  in 
such  a  way  as  to  give  increased 
capacity  to  the  pelvic  cavity. 

Coccyx  (os  coccygis). — The 
coccyx  is  usually  formed  of  four 
small  segments  of  bone,  and  is 
the  most  rudimentary  part  of 
the  vertebral  column. 


INTERCLAVlCULAR 
NOTCH 


THORAX 


FOR  THIRD  COSTAL 
CARTILAGE 


FOR  FOURTH  COSTAL 
CARTILAGE 


FIFTH  COSTAL 
CARTILAGE 


FOR  SIXTH  COSTAL 

CARTILAGE 
FOR  SEVENTH  COSTAL 

CARTILAGE 


The  thorax  is  an  elongated 
bony  cage  formed  by  the  ster- 
num and  costal  cartilages  in 
front,  the  twelve  ribs  on  each 
side,  and  the  bodies  of  the  twelve 
thoracic  vertebras  behind.  It 
contains  and  protects  the  prin- 
cipal organs  of  respiration  and 
circulation. 

Sternum,  or  breast  bone.  — 
It  is  a  flat,  narroAv  bone  about 
six  inches  long,  situated  in  the 
median  line  in  the  front  of  the 
chest,  and  may  be  likened  to  a  short,  flat  sword.  It  consists  of  three 
portions.  The  upper  part  is  termed  the  handle,  or  manubrium ;  the 
middle  and  largest  piece  is  termed  the  body,  or  gladiolus ;  the  in- 
ferior portion  is  termed  the  ensiform,  or  the  xiphoid  process.  On 
both  sides  of  the  upper  and  middle  pieces  are  notches  for  the  recep- 


FOR  ARTICULATION 
OF  CLAVICLE 


fOR  FIRST  COSTAL 
CARTILAGE 


FOR  SECOND  COSTAL 
CARTILAGE 


FIG.  51.  —  THE  STERNUM.      Ventral 
aspect.     (Gerrish.) 


78 


ANATOMY  AND  PHYSIOLOGY          [CHAP.  V 


tion  of  the  sternal  ends  of  the  costal  cartilages.  The  ensiform  or 
xiphoid  process  is  cartilaginous  in  structure  in  early  life,  but  is  more 
or  less  ossified  at  the  upper  part  in  the  adult ;  it  has  no  ribs  attached 
to  it,  but  affords  attachment  for  some  of  the  abdominal  muscles. 
Ribs  (costse).  — The  ribs,  twenty-four  in  number,  are  situated 
twelve  on  each  side  of  the  thoracic  cavity.  They  are  all  con- 
nected with  the  thoracic  vertebrae  at  the  back,  and  the  first 
seven  pairs  are  connected  with  the  sternum  in  front  through 
the  intervention  of  the  costal  cartilages.  These  first  seven  pairs 
are  called,  from  their  attachment,  the  true  ribs.  The  remaining 
five  pairs  are  termed  false  ribs.  Of  these,  the  upper  three, 


FIG.  52.  —  THE  EIGHTH  RIB  OF  THE  RIGHT  SIDE.    Viewed  from  behind.     (Gerrish.) 

eighth,  ninth,  and  tenth,  are  attached  in  front  to  the  costal 
cartilages  of  the  next  rib  above.  The  two  lowest  being  unattached 
in  front,  are  termed  floating  ribs. 

The  convexity  of  the  ribs  is  turned  outward  so  as  to  give 
roundness  to  the  sides  of  the  chest  and  increase  the  size  of  its 
cavity;  each  rib  slopes  downward  from  its  vertebral  attach- 
ment, so  that  its  sternal  end  is  considerably  lower  than  its  dorsal, 
and  the  lower  border  is  grooved  for  the  accommodation  of  the 
intercostal  nerves  and  blood-vessels.  The  spaces  left  between  the 
ribs  are  called  the  intercostal  spaces. 

BONES  OF  THE  UPPER  EXTREMITIES 

Clavicle  (clavicula,  or  collar  bone)  ...       2 

Scapula  (shoulder  blade)         2 

Humerus  (arm) 2 

Ulna  — 2     1 

(torearm) 4/64 


Radius  —  2 

Carpus  (wrist) 16 

Metacarpus  (palm  of  hand) 10 

Phalanges  (fingers) 28, 


CHAP.  V] 


THE  SKELETON 


79 


Clavicle,  or  collar  bone.  —  It  is  a  long  bone,  placed  horizontally 
above  the  thorax.  It  articulates  with  the  sternum  by  its  inner 
extremity,  which  is  called  the  sternal  extremity.  Its  outer  or 
acromial  extremity  articulates  with  the  scapula.  In  the  female, 
the  clavicle  is  generally  less  curved,  smoother,  shorter,  and  more 


FIG.  53.  —  THE  RIGHT  CLAVICLE.     Upper  surface.     (Gerrish.) 

slender  than  in  the  male.  In  those  persons  who  perform  consider- 
able manual  labor,  which  brings  into  constant  action  the  muscles 
connected  with  this  bone,  it  acquires  considerable  bulk. 

Scapula,  or  shoulder  blade.  —  It  is  a  large,  flat  bone,  triangular 
in  shape,  placed  between  the  second  and  eighth  ribs  on  the  back 
part  of  the  thorax.  It  is  unevenly  divided  on  its  dorsal  surface 


Spine 


Coracoid  process 


Acromion  process 


Glenoid  cavity 


FIG.  54.  —  THE  RIGHT  SCAPULA,  OR  SHOULDER  BLADE.     (Morrow.) 


80 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  V 


by  a  very  prominent  ridge,  the  spine  of  the  scapula,  which  termi- 
nates in  a  large  triangular  projection  called  the  acromion  process 
or  summit  of  the  shoulder.  Below  the  acromion  process,  at  the 
head  of  the  shoulder  blade,  is  a  shallow  socket,  the  glenoid  cavity, 
which  receives  the  head  of  the  humerus. 

Humerus,  or  arm  bone.  —  The  humerus  is  the  longest  bone  of 
the  upper  limb.     The  upper  extremity  of  the  bone  consists  of  a 


Anatomical  nee 
Greater  tuberosity 


Condyles 


FIG.  55.  —  THE  LEFT  HUMERUS,  OR  ARM 
BONE.     (Morrow.) 


tyloid 
process 


FIG.  56.  —  THE  BONES  OF  THE 
RIGHT  FOREARM.  Anterior  view. 
(Morrow.) 


rounded  head  joined  to  the  shaft  by  a  constricted  neck,  and  of 
two  eminences  called  the  larger  and  smaller  tubercles,  also  known 
as  tuberosities.  The  head  articulates  with  the  glenoid  cavity  of 
the  scapula.  The  constricted  neck  above  the  tubercles  is  called 
the  anatomical  neck,  and  that  below  the  tubercles,  the  surgical 
neck,  because  it  is  so  often  fractured.  The  lower  extremity  of 


CHAP.  V] 


THE  SKELETON 


81 


the  bone  is  flattened  from  before  backward  into  a  broad  articular 
surface  called  the  trochlea  which  is  divided  by  a  slight  ridge  so 
that  it  ends  in  two  condyles  by  means  of  which  it  articulates  with 
the  radius  and  ulna. 

Ulna,  or  elbow  bone.  —  It  is  placed  at  the  inner  side  (little 
ringer  side)  of  the  forearm,  parallel  with  the  radius.  Its  upper 
extremity  presents  for  examination  two  large  curved  processes 
and  two  concave 
cavities;  the  larger 
process  forms  the 
head  of  the  elbow, 
and  is  called  the 
olecranon  process. 
The  smaller  process 
on  the  front  sur- 
face is  termed  the 
coronoid,  and  the 
trochlea  of  the 
humerus  fits  into 
the  cavity  —  the 
great  sigmoid  cav- 
ity — between  these 
two  processes.  The 
lesser  sigmoid  cav- 
ity is  on  the  outer 
side  of  the  coronoid, 
and  receives  the 
head  of  the  radius. 
The  lower  extremity 
of  the  ulna  is  of 

small  size  and  ends  in  two  prominences;  the  outer  one,  called 
the  head,  articulates  with  the  radius ;  the  inner  one,  named  the 
styloid  process,  serves  for  the  attachment  of  ligaments  from  the 
wrist;  but  the  ulna  is  excluded  from  the  wrist  by  a  piece  of 
fibro-cartilage. 

Radius.  —  It  is  situated  on  the  outer  side  of  the  forearm. 
The  upper  end  is  small  and  rounded,  with  a  shallow  depression  on 
its  upper  surface  for  articulation  with  the  humerus,  and  a  promi- 
nent ridge  about  it,  like  the  head  of  a  nail,  by  means  of  which  it 
G 


THIRD  PHALANX 


FIG.  57.  —  THE  BONES  OF  THE  RIGHT  HAND. 
Palmar  aspect.     (Gerrish.) 


82  ANATOMY  AND   PHYSIOLOGY          [CHAP.  V 

rotates  within  the  lesser  sigmoid  cavity  of  the  ulna.     The  lower 
end  of  the  radius  is  large,  and  forms  the  chief  part  of  the  wrist. 

Carpus,  or  wrist.  —  The  wrist  joint  is  composed  of  eight  small 
bones  (ossa  carpi)  united  by  ligaments ;  they  are  arranged  in  two 
rows,  and  are  closely  welded  together,  yet  by  the  arrangement 
of  their  ligaments  allow  of  a  certain  amount  of  motion.  They 
afford  origin  by  their  palmar  surface  to  most  of  the  short  muscles 
of  the  thumb  and  little  finger,  and  are  named  as  follows :  — 

1st  row.     Scaphoid  ...  1  2d  row.     Trapezium  ...  1 

Semilunar  ...  1  Trapezoid    ...  1 

Cuneiform  ...  1  Os  Magnum     .     .  1 

Pisiform  ...  1  Unciform     ...  1 

Metacarpus,  or  body  of  hand.  —  Each  metacarpus  is  formed 
by  five  bones  (ossa  metacarpalia) .  The  bones  are  curved  longi- 
tudinally, being  convex  behind,  and  concave  in  front.  They 
articulate  at  their  bases  with  the  second  row  of  carpal  bones  and 
with  each  other.  The  heads  of  the  bones  articulate  with  the  bases 
of  the  first  row  of  the  phalanges. 

Phalanges,  or  digits.  —  They  are  the  bones  of  the  fingers, 
and  are  fourteen  in  number  in  each  hand,  three  for  each  finger 
and  two  for  the  thumb.  The  first  row  articulates  with  the  meta- 
carpal  bones  and  the  second  row  of  phalanges ;  the  second  row, 
with  the  first  and  third ;  and  the  third,  with  the  second  row. 

BONES  OF  THE   LOWER  EXTREMITIES 

Hip  bones  (ossa  coxae  or  ossa  innominata)     ...  2 

Femur  (thigh  bone) 2 

Patella  (knee-cap) 2 

Tibia  (shin  bone)   2 


Fibula  (calf  bone)  2  j   leg       '.    ' 

Tarsus  (ankle,  or  root  of  foot) 14 

Metatarsus  (sole  and  instep)  . 10 

Phalanges  (toes) 28 , 

The  bones  of  the  lower  extremities  correspond  to  a  great  extent 
with  those  of  the  upper  extremities,  and  bear  a  rough  resemblance 
to  them,  but  are  heavier  and  more  firmly  knit  together. 

Hip  bone,  or  os  coxa.  —  It  is  a  large,  irregularly  shaped  bone 
which,  with  its  fellow  of  the  opposite  side,  forms  the  sides  and 


CHAP.  V] 


THE  SKELETON 


83 


front  wall  of  the  pelvic  cavity.  In  young  subjects  it  consists  of 
three  separate  parts,  and  although  in  the  adult  these  have  become 
united,  it  is  usual  to  describe  the  bone  as  divisible  into  three  por- 
tions:  (1)  the  ilium  (plural  ilia),  (2)  the  ischium  (plural  ischii), 
(3)  the  pubis  (plural  pubes). 

The  ilium  is  the  upper  broad  and  expanded  portion  which  forms 
the  prominence  of  the  hip.  The  ischium  is  the  lower  and  strongest 
portion  of  the  bone,  while  the  pubis  is  that  portion  which  helps 
to  form  the  front  of  the  pelvis. 
Where  these  three  portions  of 
the  bone  meet  and  finally  anky- 
lose,  is  a  deep  socket,  called  the 
acetabulum,  into  which  the  head 
of  the  femur  fits.  Other  points 
of  special  interest  to  note  in  the 
hip  bones  are  :  — 

(1)  The  spinous  process  formed 
by  the  projection  of  the  crest  of 
the  ilium  in  front,  which  is  called 
the    anterior    superior    spinous 
process,   and   which   is    a   well- 
known    and    convenient    land- 

.     .  ,  .  -ii        FIG.  58.  —  DEVELOPMENT  OF  THE  HIP 

mark  in  making  anatomical  and  BONE.    Showing  the  union  of  the  three 

Surgical  measurements.  portions  in  the  acetabulum.     (Gerrish.) 

(2)  The  largest  foramen  in  the  skeleton,  known  as  the  thyroid 
foramen,  situated  between  the  ischium  and  pubis. 

(3)  The  symphysis  pubis,   or  pubic  articulation,    which    also 
serves  for  a  convenient  landmark  in  making  measurements. 

The  pelvis.  —  The  pelvis,  so  called  from  its  resemblance  to  a 
basin,  is  stronger  and  more  massively  constructed  than  either  the 
cranial  or  the  thoracic  cavity.  It  is  composed  of  four  bones,  the 
two  hip  bones  forming  the  sides  and  front,  the  sacrum  and  coccyx 
completing  it  behind.  It  is  divided  by  a  narrowed  bony  ring  into 
the  large  (false),  and  small  (true)  pelvis.  The  narrowed  bony 
ring  which  is  the  dividing  line  is  spoken  of  as  the  brim  of  the  pelvis, 
the  ilio-pectineal  line,  and  the  strait.  The  large  pelvis  is  all  that 
expanded  portion  of  the  pelvis  situated  above  the  brim ;  it  forms 
an  incomplete  or  false  basin.  The  small  pelvis  is  all  that  portion 
situated  below  the  brim.  Its  cavity  is  a  little  wider  in  every 


84 


ANATOMY  AND  PHYSIOLOGY          [CHAP.  V 


FIG.  59.— FEMALE  PELVIS. 


direction  than  the  brim  itself,  while  the  large  pelvis  is  a  great  deal 
wider.  The  small  bony  pelvis  is  a  basin  with  incomplete  walls 
of  bone,  the  bottom  of  which  is  composed  of  the  softer  tissues, 
muscles,  and  ligaments.  The  opening  of  the  small  pelvis,  i.e.,  the 


FIG.  60.  —  MALE  PELVIS. 


CHAP.  V] 


THE   SKELETON 


85 


space  just  above  the  brim,  is  called  the  inlet,  and  the  opening 
below  is  called  the  inferior  strait,  or  outlet. 

The  female  pelvis  differs  from  that  of  the  male  in  those  particu- 
lars which  render  it  better  adapted  to  pregnancy  and  parturition. 
It  is  more  shallow  than  the  male  pelvis,  but  wider  in  every  direc- 
tion. The  inlet  and  outlet  are  larger,  the  bones  are  lighter  and 
smoother,  and  the  coccyx  is 

more  movable.     As  can  be  ^&*    ^^  ^~~  Head 

seen  by  looking  at  Fig.  59 
and  Fig.  60  a  distinctive 
anatomical  difference  is  that 
the  sub-pubic  angle  in  a 
male  is  less  than  a  right 
angle,  and  in  the  female  it 
is  greater  than  a  right  angle. 

Femur,  or  thigh  bone.  - 
It  is  the  longest,  and  strong- 
est bone  in  the  skeleton. 
The  upper  extremity  of  the 
femur,  like  that  of  the 
humerus,  consists  of  a 
rounded  head  joined  to  the 
shaft  by  a  constricted  neck, 
and  of  two  eminences,  called 
the  greater  and  lesser  tro- 
chanters.  The  head  articu- 
lates with  the  cavity  in 
the  hip  bone,  called  the 
acetabulum.  The  lower 
extremity  of  the  femur  is 
larger  than  the  upper,  is 
flattened  from  before  back- 
wards, and  divided  into  two 
large  eminences  or  condyles  by  an  intervening  notch.  It  articu- 
lates with  the  tibia  and  the  patella,  or  knee-cap.  In  the  erect 
position  it  is  not  vertical,  being  separated  from  its  fellow  by 
a  considerable  interval,  which  corresponds  to  the  entire  breadth 
of  the  pelvis,  but  the  bone  inclines  gradually  downward  and 
inward,  so  as  to  approach  its  fellow  towards  its  lower  part, 


Condyles 

FIG.  61.  —  THE  RIGHT  FEMUR,  OR  THIGH 
BONE.     Anterior  view.     (Morrow.) 


86 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  V 


BASE 


in  order  to  bring  the  knee-joint   near  the   line  of   gravity  of 
the  body.     The  degree  of  inclination  varies  in  different  persons, 

and  is  greater  in  the  female 
than  the  male,  on  account  of 
the  greater  breadth  of  the 
pelvis. 

Patella,  or  knee-cap.  —  It 
is  the  largest  sesamoid  bone 
in   the   body.      It    is    small, 
flat,  triangular  in  shape,  and 
AP!EX  placed  in  front  of  the  knee- 

FIG.  62.  —  THE  RIGHT  PATELLA.     Ventral    joint,      which      it      serves      to 

protect.     (See   Fig.   30.)     It 

articulates  with  the  two  condyles  of  the  femur,  and  is  separated 
from  the  skin  by  a  bursa.     (See  page  143.) 

Tibia,  or  shin  bone.  —  It  is  situated  at  the  front  and  inner  side 
of  the  leg.  The  upper  ex- 
tremity is  large,  and  expanded 
into  two  lateral  eminences  with 
concave  surfaces,  which  re- 
ceive the  condyles  of  the 
femur.  The  lower  extremity 
is  much  smaller  than  the 
upper;  it  is  prolonged  down- 
ward on  its  inner  side  into  a 
strong  process,  the  inner,  or 
medial,  malleolus.  It  articu- 
lates with  the  fibula  and  one 
of  the  bones  of  the  ankle.  (In 
the  male,  its  direction  is  verti- 
cal and  parallel  with  the  bone 
of  the  opposite  side;  but  in 
the  female  it  has  a  slightly 
oblique  direction  outward,  to 
compensate  for  the  oblique  di- 
rection of  the  femur  inward.) 

Fibula,  or  calf  bone.  —  It  is 
situated  at  the  outer  side  of 
the  leg.  It  is  the  smaller  of 


Outer 
malleolus 


I<IG.  C3.  —  THE  BONES  OF  THE  RIGHT 

LEG.    (Morrow.) 


CHAP.  V] 


THE   SKELETON 


87 


the  two  bones,  and,  in  proportion  to  its  length,  the  most  slender 
of  all  the  long  bones ;  it  is  placed  nearly  parallel  with  the  tibia. 
The  upper  extremity 
consists  of  an  irregu- 
lar quadrate  head  by 
means  of  which  it  ar- 
ticulates with  the  tibia. 
The  lower  extremity 
is  prolonged  down- 
ward into  a  pointed 
process,  the  external,  or 
lateral,  malleolus,  which 
lies  just  beneath  the 
skin.  It  articulates 
with  the  tibia  and  one 
of  the  bones  of  the 
ankle. 

Tarsus.— The  tarsus 
is  composed  of  seven 
small  bones  united  by 
ligaments,  but  the  tar- 
sal  bones  differ  from 
the  carpal  in  being 
larger  and  more  ir- 
regularly shaped.  The 
largest  and  strongest 
of  the  tarsal  bones  is 
called  the  calcaneum, 
or  heel  bone  ;  it  serves 
to  transmit  the  weight  of  the  body  to  the  ground,  and  forms  a 
strong  lever  for  the  muscles  of  the  calf  of  the  leg.  The  names 
are  as  follows  :  — 


FIRST   PHALANX 
OF  FIFTH  TOE 


FIRST  PHALANX 
.OF  HALLUX 


FIG.  64.  —  THE  BONES  OF  THE  RIGHT  FOOT. 
Viewed  from  above.     (Gerrish.) 


Calcaneum  .  .  . 
Astragalus  .  .  . 
Cuboid  .... 
Scaphoid.  .  .  . 
External  cuneiform 
Middle  cuneiform . 
Internal  cuneiform 


88 


ANATOMY  AND  PHYSIOLOGY          [CHAP.  V 


Metatarsus,  or  sole  and  instep  of  foot.  —  The  metatarsus  is 
formed  by  five  bones  which  closely  resemble  the  metacarpal  bones 
of  the  hand.  Each  bone  articulates  with  the  tarsal  bones  by 
one  extremity,  and  by  the  other  with  the  first  row  of  phalanges.  ' 

Phalanges,  or  digits.  —  Both  in  number  and  general  arrange- 
ment resemble  those  in  the  hand,  there  being  two  in  the  great  toe 
and  three  in  each  of  the  other  toes. 


Function 


Bones 


Classification 


SUMMARY 

1.  Organs  of  support. 

2.  Instruments  of  locomotion. 

3.  Framework  of  hard  material. 

4.  Afford  attachment  to  soft  parts. 

5.  Shelter  delicate  structures. 

6.  Shape  to  whole  body. 

1.  Long. 

2.  Short. 

3.  Flat. 

4.  Irregular. 


TABLE  OF  THE  BONES 


HEAD 


Cranium 

Occipital 1 

Parietal 2 

Frontal        1 

Temporal 2 

Sphenoid 1 

Ethmoid 1 

8 


Face 

Nasal 2 

Lacrimal 2 

Vomer 1 

Malar 2 

Palate  ..." 2 

Inferior  turbinated      ...  2 

Maxilla 2 

Mandible 1 

14 


I  Malleus     . 2 

Ear  <  Incus 2 

[Stapes       2 

6 

Hyoid  bone  in  the  neck 1 


CHAP.  V] 


SUMMARY 


TRUNK 


Vertebrae 


[Cervical   .... 

Child 
....       7 

Adult 

7 

Thoracic  .... 

....     12 

12 

Lumbar    .... 

.     .     .     .       5 

5 

Sacral       .... 

5 

1 

Coccygeal 

4-33 

1  —  26 

Ribs    

.     .     .          24 

Sternum  . 

Upper  Extremity 

Clavicle , 

Scapula 

Humerus 

Ulna 

Radius 


Carpus 


Scaphoid   . 
Semilunar 
Cuneiform 
Pisiform    . 
Trapezium 
Trapezoid 
Os  magnum 
Unciform 

Metacarpus    .     ,     . 

Phalanges  .... 


14 
32 


32x2-64 


51 

Lower  Extremity 
Hip  bone  (os  coxa)      ...       1 

Femur 1 

Patella 1 

Tibia 1 

Fibula       1 

Calcaneum  ...  1 
Astragalus  ...  1 
Cuboid  ....  1 
Tarsus  {  Scaphoid  ....  1 
External  cuneiform  1 
Middle  cuneiform  .  1 
Internal  cuneiform  1 

Metatarsus 5 

Phalanges      .     .     .     .     .     -14 

3l 

31X2  =  62 


CHAPTER  VI 

JOINTS    OR  ARTICULATIONS 

Joints  or  articulations.  —  The  various  bones  of  which  the 
skeleton  consists  are  connected  at  different  parts  of  their  surfaces, 
and  such  connections  are  called  joints  or  articulations. 

CLASSIFICATION 

Joints  are  classified  according  to  the  amount  of  movement  of 
which  they  are  capable. 

1.  Immovable  joints  or  synarthroses. 

2.  Slightly  movable  joints,  or  amphiarthroses. 

3.  Freely  movable  joints,  or  diarthroses. 

In  all  instances  some  softer  substance  is  placed  between  the 
bones,  uniting  them  or  clothing  the  opposed  surfaces;  but  the 
manner  in  which  the  several  pieces  of  the  skeleton  are  thus 
connected  varies  to  a  great  degree. 

IMMOVABLE  JOINTS,   OR  SYNARTHROSES 

The  bones  are  connected  by  fibrous  tissue  or  cartilage. 

The  bones  of  the  cranium  and  the  facial  bones  (with  the  ex- 
ception of  the  lower  jaw)  have  their  adja- 
cent surfaces  applied  in  close  contact,  with 
only  a  thin  layer  of  fibrous  tissue  placed 
between  their  margins. 

In  most  of  the  cranial  bones  this  union 
occurs  by  means  of  toothed  edges  which 
dovetail  into  one  another  and  form  jagged 

FIG.  65.— A  TOOTHED,        ]mes  of  union  known  as  SUturCS. 
OR  DENTATED,  SUTURE. 

1  he  three  most  important  sutures  are  :  — 

(1)  Coronal.  —  The  line  of  union  between  the  frontal  and 
parietal  bones. 

90 


CHAP.  VI]         JOINTS  OR  ARTICULATIONS 


91 


(2)  Lambdoidal.  —  The  line  of  union  between  the  parietal  and 
occipital  bones. 

(3)  Sagittal  suture.  —  This  begins  at  the  base  of  the  nose, 


FIG.  66.  —  DIAMETERS  AND  LANDMARKS  OF  THE  FCETAL  SKULL.     Upper  surface. 

(Edgar.) 


FIG.  67.  —  DIAMETERS   AND   LANDMARKS   OF   THE  FCETAL  SKULL.     Posterior 
surface.     (Edgar.) 


92  ANATOMY  AND   PHYSIOLOGY        [CHAP.  VI 

extends  along  the  middle  line  on  the  top  of  the  crown,  separates 
the  frontal  bone  into  two  parts,1  the  parietal  bones  from  each 
other,  and  ends  at  the  posterior  fontanelle. 

Synchondrosis  is  usually  a  temporary  form  of  joint.  The 
cartilage  between  the  bones  ossifies  before  adult  life.  Example: 
the  union  of  the  sphenoid  and  occipital  bones. 

SLIGHTLY  MOVABLE  JOINTS,   OR  AMPHIARTHROSES 
The  above  terms  apply  to  joints  that  permit  of  slight  movement 
and  include  two  varieties :    (1)  symphysis  and  (2)  syndesmosis. 

Symphysis.  —  In  this  form 

BONE 

of  articulation  the  bony  sur- 
faces are  joined  together  by 
FIBR<KARTILAGE  broad,  flattened  disks  of  fibro- 
cartilage,  as  in  the  articula- 
tions between  the  bodies  of 

FIG.   68.  —  A  SLIGHTLY  MOVABLE  JOINT. 

the  vertebrae.  These  inter- 
vertebral  disks  being  compressible  and  extensile,  the  spine  can 
be  moved  to  a  limited  extent  in  every  direction.  In  the  pel- 
vis the  .articulations  between  the  two  pubic  bones  (symphysis 
pubis),2and  between  the  sacrum  and  ilia  (sacro-iliac  articulation), 
are  slightly  movable.  The  pubic  bones  are  united  by  a  disk  of 
fibro-cartilage  and  by  ligaments.  In  the  sacro-iliac  articulation 
the  sacrum  is  united  more  closely  to  the  ilia,  the  articular  surfaces 
being  covered  by  cartilage  and  held  together  by  ligaments. 

The  fibro-cartilage  between  these  joints  (symphysis  pubis  and 
sacro-iliac)  becomes  thickened  and  softened  during  pregnancy 
and  allows  of  a  certain  limited  motion  which  is  essential  to  a 
normal  parturition. 

Syndesmosis.  —  An  articulation  by  means  of  an  interosseous 
ligament,  as  in  the  lower  tibio-fibular  articulation,  is  called 
syndesmosis. 

FREELY  MOVABLE  JOINTS,   OR  DIARTHROSES 
This  division  includes  the  complete  joints,  which  are  the  only 
joints  in  which  the  three  following  conditions  are  found  :  - 

(1)  The  bones  are  united  by  fibrous  ligaments,  forming  more 

1  That  portion  of  the  sagittal  suture  which  separates  the  frontal  bone  into  two 
parts  is  often  called  the  frontal  suture.     (See  Fig.  66.) 

2  See  Fig.  59. 


CHAP.  VI]          JOINTS   OR   ARTICULATIONS 


93 


PERIOSTEUM 


SYNOVIAL   FOLD 


FIG.  69.  — A 


synovial    membrane 
dotted  lines. 


JOINT-CAVITY 


COMPLETE  JOINT.    The 
is    represented    by 


or  less  perfect  capsules.     The  ligaments  are  not  always  so  tight 

as  to  maintain  the  bones  in  close  contact  in  all  positions  of  the 

joint,  but  are  rather  tightened  in  some  positions  and  relaxed 

in  others,  so  that  in  many  cases  they  are  to  be  looked  on  chiefly 

as  controllers  of   movements, 

and  not   as  serving  solely  to 

hold  the  bones  together.     The 

bones  are  held  together  in  these 

joints   partly    by   atmospheric 

pressure  and    largely    by    the 

surrounding  muscles. 

(2)  A    secreting    membrane 
(synovial)  l    lines   the   capsule 
and  is  so  arranged  that  it  dips 
in  between  the  edges  of  the  op- 
posing articular  cartilages.  (See 
Fig.  69.) 

(3)  Each  articular  end  of  the  bone  is  covered  by  hyaline  cartilage 
which  provides   surfaces  of  remarkable   smoothness,   and  these 
surfaces  are  lubricated  by  the  synovial  fluid  secreted  from  the  deli- 
cate synovial  membrane  which  lines  the  cavity  of  the  joint. 

The  varieties  of  joints  in  this  class  have  been  determined  by 
the  kind  of  motion  permitted  in  each.     They  are  as  follows :  — 

(1)  Gliding  joint.  —  The  articular  surfaces  are  nearly  flat,  and 
admit  of  only  a  limited  amount  of  gliding  movement,  as  in  the 
joints  between  the  articular  processes  of  the  vertebrae. 

(2)  Hinge  joint.  —  The  articular  surfaces  are  of  such  shape  as 
to  permit  of  movement  to  and  fro  in  one  plane  only,  like  a  door 
on  its  hinges.     These  movements  are  called  flexion  and  extension, 
and  may  be  seen  in  the  articulation  of  the  arm  with  the  forearm, 
in  the  ankle  joint,  and  in  the  articulations  of  the  phalanges. 

(3)  Ball-and-socket  joint.  —  In  this  form  of  joint  a  more  or 
less  rounded  head  is  received  into  a  cup-like  cavity,  as  the  head 
of  the  femur  into  the  acetabulum,  and  the  head  of  the  humerus 
into  the   glenoid   cavity  of  the   scapula.     Movement  can  take 
place  freely  in  any  direction,  but  the  shallower  the  cup,  the  greater 
the   extent   of  motion.     The    shoulder  joint  is  the   most  freely 
movable  joint  in  the  body. 

1  See  page  142. 


94  ANATOMY  AND  PHYSIOLOGY         [CHAP.  VI 

(4)  Pivot  joint.  —  In  this  form,  one  bone  rotates  around  another 
which  remains  stationary,  as  in  the  articulation  of  the  atlas  with 
the  axis  (epistropheus),  and  in  the  articulation  of  the  ulna  and 
radius.     In  the  articulation  of  the  ulna,  and  radius,  the  ulna  re- 
mains stationary,  and  the  radius  rotates  freely  around  its  upper 
end.     The  hand  is  attached  to  the  lower  end  of  the  radius,  and 
the  radius,  in  rotating,  carries  the  hand  with  it;   thus,  the  palm 
of  the  hand  is  alternately  turned  forward  and  backward.     When 
the  palm  is  turned  forward,  or  upward,  the  atittude  is  called 
supination ;   when  backward,  or  downward,  pronation. 

(5)  Condyloid  joint.  —  When  an  oval-shaped  head,  or  condyle, 
of  a  bone  is  received  into  an  elliptical  cavity,  it  is  said  to  form 
a  condyloid  joint.     An  example  of  this  kind  of  joint  is  found  in 
the  metacarpo-phalangeal  articulations.     The  rounded  heads  of 
the  metacarpal  bones  are  received  in  the  elliptical-shaped  bases 
of  the  phalanges. 

(6)  Saddle  joint.  —  In  this  joint  the  articular  surface  of  each 
bone  is  concave  in  one  direction,  and  convex  in  another,  at  right 
angles  to  the  former.     A  man  seated  in  a  saddle  is  "  articulated  " 
with  the  saddle  by  such  a  joint.     For  the  saddle  is  concave  from 
before  backward,  and  convex  from  side  to  side,  while  the  man 
presents  to  it  the  concavity  of  his  legs  astride,  from  side  to  side, 
and  the  convexity  of  his  seat,  from  before  backward.     The  meta- 
carpal bone  of  the  thumb  is  articulated  with  the  trapezius  of  the 
carpus  by  a  saddle  joint.     Both  the  condyloid  and  saddle  joints 
admit  of  motion  in  every  direction  except  that  of  axial  rotation. 

Movement.  —  Bones  thus  connected  are  capable  of  the  follow- 
ing different  kinds  of  movement. 

1.  Flexion.  —  A  limb  is  flexed,  when  it  is  bent. 

2.  Extension.  —  A  limb  is  extended,  when  it  is  straightened  out. 

3.  Abduction.  —  This  term  means  drawn  away  from  the  middle 
line  of  the  body. 

4.  Adduction.  —  This  term  means  brought  to,  or  nearer  the 
middle  line  of  the  body. 

Both  abduction  and  adduction  have  a  different  meaning  when 
used  with  reference  to  the  fingers  and  toes.  In  the  hand  the 
imaginary  line  is  supposed  to  be  drawn  through  the  middle  finger; 
and  in  the  foot  through  the  second  toe. 

5.  Rotation.  -  -  Means  made  to  turn  on  its  own  axis. 


CHAP.  VI]         JOINTS  OR  ARTICULATIONS  95 

6.  Circwnduction.  —  Means  made  to  describe  a  conical  space 
by  rotation  around  an  imaginary  axis. 

No  part  of  the  body  is  capable  of  perfect  rotation,  as  a  wheel, 
for  the  simple  reason  that  such  motion  would  necessarily  tear 
asunder  all  the  vessels,  nerves,  muscles,  etc.,  which  unite  it  with 
other  parts. 

Sprain.  —  A  wrenching  or  twisting  of  a  joint  accompanied  by 
a  stretching  or  tearing  of  the  ligaments  or  tendons  is  called  a 
sprain. 

Dislocation.  —  If  in  addition  to  a  sprain,  the  bone  is  displaced, 
the  injury  is  called  a  dislocation. 


96 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  VI 


SUMMARY 

Joints  or  Articulations  —  connections  existing  between  bones. 

1.  Sutura. — Articulations   by 


Immovable 
Joint 

or 
Synarthrosis, 


Bones  are  con- 
n  e  c  t  e  d  by 
fibrous  tissue 
or  cartilage. 


pro- 


Bones  are  con-  , 

Slightly 
Movable 

nected        by 
discs   of   car-  • 

Joint 

tilage    or    in- 

or 

terosseous 

Amphiarthrosis, 

ligaments. 

1  .  Fibrous  liga- 

ment     form- 

ing a  capsule. 

Movable 

2.  Synovial 

Joint 

membrane 

or 

lining  fibrous 

Diarthrosis, 

capsule. 

3.  Hyaline  car- 

tilage   cover- 

ing   articular 

ends  of  bones. 

Movement 


Flexion. 
Extension. 
Abduction. 
Adduction. 
Rotation. 
.  Circumduction. 


cesses  and  indentations  interlocked 
together.  A  thin  layer  of  fibrous 
tissue  is  interposed  between  the 
bones.  Sutures  may  be  dentated, 
dove-tailed ;  serrated,  saw-like ; 
squamous,  scale-like ;  harmonic, 
smooth ;  and  grooved,  for  the  re- 
ception of  thin  plates  of  bone. 
2.  Synchondrosis.  --  Temporary 
joint.  Cartilage  between  bones 
ossifies  in  adult  life. 

1.  Symphysis.  —  The       bones      are 
united  by  a  plate  or  disc  of  fibro- 
cartilage  of  considerable  thickness. 

2.  Syndesmosis,  —  The  bony  surfaces 
are  united  by  an  interosseous  liga- 
ment, as  in  the  lower  tibio-fibular 
articulation. 

1.  Arthrodia.  —  Gliding  joint ;  artic- 
ulates   by    plane    surfaces    which 
glide  upon  each  other. 

2.  Ginglymus.  —  Hinge    or    angular 
joint ;    moves  backward  and  for- 
ward in  one  plane. 

3.  Enarthrosis.  —  Ball-and-socket 
joint ;    articulates  by  a  globular 
head  in  a  cup-like  cavity. 

4.  Trochoides.  —  Pivot  joint ;  articu- 
lates by  a  pivot  process  turning 
within  a  ring,  or  by  a  ring  turning 
around  a  pivot. 

5.  Condylarthrosis.  —  Condyloid 
joint ;    ovoid  head  received  into 
elliptical  cavity. 

6.  Reciprocal  Reception.  —  Saddle 
joint ;    articular  surfaces  are  con-  . 
cavo-convex. 


CHAPTER  VII 

MUSCULAR    TISSUE:    CLASSIFICATION;    FUNCTIONALLY   IMPOR- 
TANT  SKELETAL   MUSCLES 

MUSCULAR  TISSUE 

THIS  is  the  tissue  by  means  of  which  the  movements  of  the  body 
are  produced.  It  constitutes  the  fleshy  parts,  enters  into  the 
structure  of  many  of  the  internal  organs,  and  forms  from  40  to 
50  per  cent  of  the  body  weight. 

Muscular  tissue,  like  every  other  tissue,  is  composed  of  cells 
and  intercellular  substance,  with  this  special  difference,  that 
the  cells  become  elongated.  The  intercellular  substance  consists 
of  a  small  amount  of  cement,  which  helps  to  hold  the  cells  to- 
gether. The  cells  are  really  bound  into  bundles  by  a  framework 
of  reticular  tissue. 

CLASSIFICATION 

Muscle  cells  are  of  three  distinct  kinds,  and  we  therefore  dis- 
tinguish three  varieties  of  muscular  tissue :  - 

1 .  Striated  or  cross-striped  ; 

2.  Non-striated  or  plain ; 

3.  Cardiac. 

Striated  or  cross-striped  muscular  tissue.  —  This  tissue  is  called 
striated  because  it  is  distinctly  marked  by  striae,  or  parallel  cross 
stripes.     It  is  also  called  skeletal  because  it  forms  the  muscles  which 
are  attached  to  the  skeleton,  and  voluntary  because  it  is  nearly 
always  under  the  control  of  the  will.     It  is   composed  of  long 
slender  cells,  measuring  on  an  average  3-^5-  inch  (0.05  mm.)   in 
diameter,  but  having  a  length  of  an  inch  or  more. 
Each  cell  consists  of  three  distinct  elements :  - 
(1)  Contractile  substance,  forming  the  centre  and   making   up 
most  of  the  bulk  of  the  cell. 

H  97 


96 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  VI 


SUMMARY 

Joints  or  Articulations  —  connections  existing  between  bones. 

1.  Sutura. — Articulations   by 


Immovable 
Joint 

or 
Synarthrosis, 


Bones  are  con- 
n  e  c  t  e  d  by 
fibrous  tissue 
or  cartilage. 


Movement 


Flexion. 

Extension. 

Abduction. 

Adduction. 

Rotation. 

Circumduction. 


pro- 


Slightly 
Movable 

Bones  are  con- 
nected by 
discs  of  car-< 

Joint 

tilage  or  in- 

or 
Amphiarthrosis, 

terosseous 
ligaments. 

'  1.  Fibrous  liga- 

ment     form- 

ing a  capsule. 

Movable 

2.  Synovial 

Joint 

membrane 

or 

lining  fibrous 

Diarthrosis, 

capsule. 

3.  Hyaline  car- 

tilage   cover- 

ing   articular 

ends  of  bones. 

cesses  and  indentations  interlocked 
together.  A  thin  layer  of  fibrous 
tissue  is  interposed  between  the 
bones.  Sutures  may  be  dentated, 
dove-tailed ;  serrated,  saw-like ; 
squamous,  scale-like ;  harmonic, 
smooth ;  and  grooved,  for  the  re- 
ception of  thin  plates  of  bone. 
2.  Synchondrosis.  --  Temporary 
joint.  Cartilage  between  bones 
ossifies  in  adult  life. 

1.  Symphysis. —  The       bones      are 
united  by  a  plate  or  disc  of  fibro- 
cartilage  of  considerable  thickness. 

2.  Syndesmosis.  —  The  bony  surfaces 
are  united  by  an  interosseous  liga- 
ment, as  in  the  lower  tibio-fibular 
articulation. 

Arthrodia.  —  Gliding  joint ;  artic- 
ulates by  plane  surfaces  which 
glide  upon  each  other. 

2.  Ginglymus.  —  Hinge    or    angular 
joint ;    moves  backward  and  for- 
ward in  one  plane. 

3.  Enarthrosis.  —  Ball-and-socket 
joint;    articulates  by  a  globular 
head  in  a  cup-like  cavity. 

4.  Trochoides.  —  Pivot  joint ;  articu- 
lates by  a  pivot  process  turning 
within  a  ring,  or  by  a  ring  turning 
around  a  pivot. 

5.  Condylarthrosis.  —  Condyloid 
joint ;    ovoid  head  received  into 
elliptical  cavity. 

6.  Reciprocal  Reception.  —  Saddle 
joint ;   articular  surfaces  are  con-  . 
cavo-convex. 


(  1 


CHAPTER  VII 

MUSCULAR    TISSUE:    CLASSIFICATION;    FUNCTIONALLY   IMPOR- 
TANT  SKELETAL   MUSCLES 

MUSCULAR  TISSUE 

THIS  is  the  tissue  by  means  of  which  the  movements  of  the  body 
are  produced.  It  constitutes  the  fleshy  parts,  enters  into  the 
structure  of  many  of  the  internal  organs,  and  forms  from  40  to 
50  per  cent  of  the  body  weight. 

Muscular  tissue,  like  every  other  tissue,  is  composed  of  cells 
and  intercellular  substance,  with  this  special  difference,  that 
the  cells  become  elongated.  The  intercellular  substance  consists 
of  a  small  amount  of  cement,  which  helps  to  hold  the  cells  to- 
gether. The  cells  are  really  bound  into  bundles  by  a  framework 
of  reticular  tissue. 

CLASSIFICATION 

Muscle  cells  are  of  three  distinct  kinds,  and  we  therefore  dis- 
tinguish three  varieties  of  muscular  tissue :  - 

1 .  Striated  or  cross-striped  ; 

2.  Non-striated  or  plain ; 

3.  Cardiac. 

Striated  or  cross-striped  muscular  tissue.  —  This  tissue  is  called 
striated  because  it  is  distinctly  marked  by  striae,  or  parallel  cross 
stripes.     It  is  also  called  skeletal  because  it  forms  the  muscles  which 
are  attached  to  the  skeleton,  and  voluntary  because  it  is  nearly 
always  under  the  control  of  the  will.     It  is   composed  of  long 
slender  cells,  measuring  on  an  average  3-^  inch  (0.05  mm.)   in 
diameter,  but  having  a  length  of  an  inch  or  more. 
Each  cell  consists  of  three  distinct  elements :  — 
(1)  Contractile  substance,  forming  the  centre  and   making   up 
most  of  the  bulk  of  the  cell. 

H  97 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  VII 


(2)  Nuclei,  which  lie  scattered  upon  the  surface  of  the  contrac- 
tile substance; 

(3)  The  sarcolemma,  a  thin,  structureless  tube  which  tightly 
encloses  the  contractile  substance  and  the  nuclei. 

As  each  cell  contains  a  number  of  nuclei,  we  may  regard  it  as  a 
multinuclear  cell  of  elongated  form.  The  muscle  cells  lie  closely 
packed,  their  ends  lapping  over  on  to  adjacent 
cells  and  forming  bundles.  Delicate  reticular 
tissue  penetrates  between  the  cells,  surrounds  the 
small  bundles  and  groups  them  into  larger  bundles. 
Reticular  tissue  also  surrounds  the  larger  bundles 
and  forms  a  covering  for  the  whole  muscle.  Thus 
it  will  be  seen  that  reticular  tissue  forms  a  sup- 
porting framework  for  muscular  tissue. 

Skeletal  Muscles.  —  The  muscles  are  separate 
organs,  each  muscle  having  its  own  sheath  of 
connective  tissue,  called  epimysium.  They  vary 
in  size  from  a  fraction  of  an  inch  to  nearly 
twenty-four  inches  (60  cm.)  and  are  very  diverse 
in  form.  In  the  trunk  the  muscles  are  broad, 
flattened,  and  expanded,  forming  the  walls  of 
the  cavities  which  they  enclose.  In  the  limbs 
they  are  of  considerable  length,  forming  more  or 
less  elongated  straps.  A  typical  muscle  is  described  as  consisting 
of  a  body  and  two  extremities.  The  body  is  the  red  contracting 
part,  and  the  extremities  are  the  ends  where  they  are  attached. 
Attachment  of  the  muscles  to  the  skeleton.  —  Muscles  are  at- 
tached to  the  bones,  cartilages,  ligaments,  and  skin  in  various 
ways,  the  most  common  mode  of  attachment  being  by  means  of 
tendons.  The  muscle  fibres  converge  as  they  approach  their 
tendinous  extremities,  and  gradually  blend  with  the  fibres  of  the 
tendons,  the  tendons  in  their  turn  inserting  their  fibres  into  the 
bones.  Where  one  muscle  connects  with  another,  each  muscle 
ends  in  expanded  form  in  a  flat,  fibrous  membrane  called  an 
aponeurosis.  Again,  in  some  cases,  the  muscles  are  connected 
with  the  bones,  cartilages,  and  skin,  without  the  intervention  of 
tendons  or  aponeuroscs. 

Fasciae.  — As  previously  stated  (page  47),  most  of  the  muscles 
are  closely  covered  by  sheets  of  fibrous  tissue  called  fasciae.     These 


FIG.  70.— DIA- 
GRAM OF  MUSCLE 
CELL  WITH  SAR- 
COLEMMA AT- 
TACHED. 


CHAP.  VII] 


MUSCULAR  TISSUE 


.99 


fasciae  not  only  envelop  and  bind  down  the  muscles,  but  also  sep- 
arate them  into  groups.  Such  groups  are  named  according  to 
the  parts  of  the  body  where  they  are  found,  viz. :  cervical  fascia, 
thoracic  fascia,  abdominal  fascia,  pelvic  fascia,  etc.  Individual 
fasciae  are  frequently  given  the  names  of  the  muscles  which  they 
envelop  and  bind  down,  viz. :  temporal  fascia,  pectoral  fascia, 
deltoid  fascia,  etc.  It  is  important  for  the  student  to  realize 
the  continuity  of  the  fibrous  membranes.  Tendons,  ligaments, 
and  fasciae  blend  with  periosteum ;  tendons  and  fasciae  serve  as 
ligaments ;  tendons  lose  themselves  in  fasciae ;  and  tendons  of  some 
muscles  serve  as  fasciae  for  others. 

Annular  ligaments.  —  In  the  vicinity  of  the  wrist  and  ankle, 
parts  of  the  deep  fascia  become  blended  into  tight  transverse 
bands,  which  serve'to  hold  the  tendons  close  to  the  bones.  These 
bands  are  called  annular  ligaments.  (See  Fig.  89.) 

Origin  and  insertion.  —  It  is  customary  to  speak  of  the  attach- 
ments of  the  opposite  ends  of  muscles  under  the  names  of  origin 
and  insertion,  the  first  term  origin  being 
usually  applied  to  the  more  fixed  attachment ; 
the  second  term  insertion  being  applied  to  the 
more  movable  attachment.  The  origin  is, 
however,  absolutely  fixed  in  only  a  very  small 
number  of  muscles,  such  as  those  of  the  face, 
which  are  attached  by  one  end  to  the  bone, 
and  by  the  other  to  the  movable  skin.  In  the 
greater  number,  the  muscle  can  act  from  either 
end. 

Non-striated  or  plain  muscular  tissue.  - 
This  tissue  is  called  plain  or  non-striated  be- 
cause it  does  not  exhibit  parallel  transverse 
striae  or  stripes.  It  is  also  called  visceral  be- 
cause it  constitutes  a  large  portion  of  the  sub- 
stance of  many  of  the  viscera,  and  involuntary 
because  it  is  usually  withdrawn  from  the  con- 
trol of  the  will.  It  is  composed  of  elongated 
cells  containing  a  single  elongated  nucleus. 
These  cells  are  always  much  shorter  than  the  cells  of  striated 
tissue.  They  lie  side  by  side  or  lap  over  one  another  at  the  ends 
and  are  joined  together  by  a  small  amount  of  cement  substance. 


FIG.  71.  —  ELON- 
GATED CELLS^OF 
PLAIN  MUSCULAR 
TISSUE.  (Highly 
magnified.) 


100  ANATOMY  AND  PHYSIOLOGY       [CHAP.  VII 

The  cells  are  variously  grouped  in  different  parts  of  the  body; 
sometimes  crowded  together  in  solid  bundles  which  are  arranged 
in  layers  and  surrounded  by  reticular  tissue,  as  in  the  intestines ; 
sometimes  arranged  in  narrow,  interlacing  bundles,  as  in  the 
bladder;  sometimes  wound  in  layers  around  the  blood-vessels; 
and  again  running  in  various  directions  and  associated  with  bands 
of  reticular  tissue,  they  form  large,  compact  masses,  as  in  the 
uterus. 

Cardiac  muscular  tissue.  —  This  variety  of  muscular  tissue  is 
found  only  in  the  heart  substance.  It  is  involuntary,  but  is  stri- 
ated, though  not  as  distinctly  as  skeletal  muscle.  It  is  made  up 
of  cells  which  are  short,  contain  just  one  nucleus,  and  no  sarco- 
lemma.  The  cells  are  grouped  in  bundles  which  are  nearly  square, 
and  fine  fibrils  from  each  cell  help  to  hold  the  bundles  together. 
The  bundles  are  mainly  held  by  reticular  tissue,  which  forms 
a  supporting  framework  in  the  heart,  just  as  it  does  in  skeletal 
and  visceral  muscle. 

Characteristics.  —  Muscular  tissue  is  highly  specialized  and 
exhibits  irritability,  contractility,  extensibility,  elasticity,  and 
tonicity. 

Irritability  has  been  defined  as  the  response  of  a  tissue  to  a 
stimulus..  All  cells  possess  this  property;  nerve  tissue,  ciliated 
epithelial  cells,  and  muscular  tissue  in  a  marked  degree.  The 
response  of  any  tissue  to  stimulation  is  to  perform  its  special 
function,  and  in  the  case  of  muscular  tissue  this  response  takes  the 
form  of  contraction. 

Contractility  is  the  power  which  enables  muscles  to  change  their 
shape  so  as  to  become  shorter  and  thicker.  It  is  possessed  to 
some  degree  by  all  living  protoplasm,  but  is  highly  developed  in 
muscular  tissue,  the  sum  of  the  contractions  of  such  tissue  result- 
ing in  motion.  Muscular  contractility  takes  place  along  definite 
lines  corresponding  to  the  long  axes  of  the  cells.  The  shortening 
is  the  essential  part  and  the  thickening  incidental.  The  function 
of  the  reticular  framework  is  passive  and  may  be  likened  to  that  of 
a  harness,  through  which  all  the  numerous  contractile  cells  are 
enabled  to  unite  their  efforts. 

Extensibility  of  a  living  muscle  means  that  it  can  be  stretched 
or  extended,  and  elasticity  means  that  it  readily  returns  to  its  orig- 
inal form.  Normally,  the  skeletal  muscles  are  in  a  condition  of 


CHAP.  VII]  MUSCULAR  TISSUE  101 

slight  tension,  being  stretched  from  bone  to  bone.  This  condition 
is  of  importance  in  two  ways :  (1)  smoothness  of  movement  is 
dependent  upon  it;  (2)  a  stretched  muscle  will  contract  more 
quickly  than  one  that  is  relaxed.  To  understand  the  first  state- 
ment it  is  important  to  remember  that  skeletal  muscles  are  usually 
arranged  in  antagonistic  groups,  one  of  which  opposes  the  other. 
Thus  the  muscles  located  on  the  anterior  surface  of  the  arm  and 
forearm  are  called  flexors,  and  those  located  on  the  posterior  sur- 
face are  called  extensors.  The  action  of  the  flexors  is  to  bend  the 
arm,  the  action  of  the  extensors  is  to  extend  or  straighten  the  arm. 
When  stimulated,  either  group  of  muscles  must  overcome  the 
resistance  of  the  opposing  group.  Therefore  contraction  takes 
place  more  slowly  and  evenly,  and  smoothness  of  movement  is 
the  result. 

Tonicity  is  the  constant  and  insensible  tendency  to  contract 
which  exists  under  normal  conditions.  It  is  really  a  mild,  sustained 
contraction,  and  though  it  may  vary  in  degree,  it  is  rarely  absent 
altogether.  Tone  in  the  skeletal  muscles  gives  them  a  certain 
firmness  and  maintains  a  slight  steady  pull  upon  their  attach- 
ments. It  is  not  likely  to  result  in  movement  on  account  of  the 
action  of  an  antagonistic  muscle.  In  fractures  the  over-riding  of 
the  broken  ends  of  a  bone  is  often  due  to  the  contraction  of  the 
muscle  that  is  the  result  of  its  tonicity. 

Function.  —  The  function  of  muscles  is  to  contract,  and  the 
functional  value  of  muscles  depends  upon  this  property.  The  con- 
traction of  a  number  of  muscles  is  expressed  in  motion.  Accord- 
ingly, contraction  is  the  means  by  which  all  the  various  muscular 
activities  of  the  body  are  made  possible. 

Stimuli.  —  This  term  is  used  to  describe  influences  which 
stimulate  muscle  cells.  They  may  be  chemical,  mechanical, 
thermal,  electrical,  or  nervous.  From  the  standpoint  of  physi- 
ology the  nervous  impulse  is  the  most  important. 

Varieties  of  muscular  movements.  —  According  to  their  causa- 
tion we  divide  muscular  movements  into  two  classes ;  voluntary, 
and  involuntary  or  automatic.  (1)  The  movements  of  the  skeletal 
muscles  (voluntary)  are  all  due  to  influences  brought  to  bear 
through  the  central  nervous  system.  Every  step  that  we  take  is 
the  result  of  a  distinct  act  on  the  part  of  a  nerve  centre  in  the 
brain.  (2)  On  the  contrary  the  contractions  of  the  heart  are  due 


102  ANATOMY  AND   PHYSIOLOGY       [CHAP.  VII 

to  an  inherent  rhythmic  tendency  of  the  muscle  itself.  We  ex- 
press this  fact  by  saying  that  cardiac  muscle  is  automatic,  and  the 
same  is  true  in  a  general  way  of  all  visceral  muscles  (involuntary). 
We  must  become  familar  with  the  idea  that  stimuli  from  the 
nervous  system  not  only  excite  muscular  activity  (as  in  the  skeletal 
muscles)  but  also  increase  or  decrease  the  degree  of  activity. 
The  influence  of  the  nervous  system  on  the  activity  of  automatic 
muscular  tissue  is  the  latter,  i.e.,  to  increase  or  decrease  it. 

Nerves.  —  Muscular  tissue  is  well  supplied  with  nerves.  Cer- 
tain nerves  convey  impulses  from  the  central  nervous  system  to  the 
muscles  and  control  their  contraction.  These  are  called  motor 
nerves.  Certain  other  nerves  have  sensory  end  organs  in  the 
muscles.  These  convey  to  the  central  nervous  system  the  state 
of  contraction  of  the  muscle  and  hence  are  called  sensory  nerves. 
By  means  of  these  sets  of  nerves  coordinated  activities  of  groups 
of  muscles  are  brought  about.1 

Conditions  of  contraction.  —  Skeletal  muscle  is  essentially  a 
quick-acting  tissue.  It  contracts  quickly  and  relaxes  promptly. 
In  sharp  contrast  to  this,  the  contractions  of  visceral  muscle  de- 
velop slowly,  are  maintained  for  some  time,  and  fade  out  slowly. 
The  contraction  of  any  one  muscle  is  the  result  of  a  series  of 
stimuli  discharged  rhythmically  by  the  nerve  cells  innervating 
it.  If  one  of  these  contractions  is  analyzed  it  will  be  found  that 
there  is  a  brief  period  after  the  muscle  is  stimulated  before  it 
contracts.  This  is  called  the  latent  period  and  is  followed  by  a 
period  of  contraction,  which  in  turn  is  followed  by  a  period  of 
relaxation.  If  we  give  0.10  of  a  second  as  the  reaction  time  of  a 
given  muscle,  0.01  might  represent  the  latent  period,  0.04  the  con- 
traction period,  and  0.05  the  relaxation  period.  It  is  easy  to  un- 
derstand how  this  might  vary,  depending  upon  (1)  the  strength  of 
the  stimuli ;  (2)  the  duration  of  the  stimulus ;  (3)  the  quality  of 
the  muscle  substance ;  and  (4)  the  temperature.  Muscles  do  their 
best  work  at  a  certain  optimum  temperature  which  differs  somewhat 
for  different  muscles.  If  the  temperature  is  raised  beyond  a  cer- 
tain upper  limit  the  muscle  loses  its  irritability  and  becomes 
functionally  depressed,  entering  finally  the  state  of  heat  rigor,  i.e., 
a  condition  of  permanent  shortening. 

Tetanus.  —  When  a  muscle  receives  a  series  of  repeated  stimuli 

1  See  "Muscle  sense,"  Chapter  XX. 


CHAP.  VII]  SKELETAL   MUSCLES  103 

so  rapidly  that  there  are  no  periods  of  relaxation,  it  remains  in  a 
condition  of  contraction  as  long  as  the  stimuli  are  sent  in,  or  until 
it  loses  its  irritability  from  fatigue.  A  contraction  of  this  kind 
is  described  as  a  compound  contraction  or  tetanus. 

Blood  supply  and  source  of  energy.  —  All  varieties  of  muscular 
tissue  are  well  supplied  with  blood-vessels  which  are  supported 
and  carried  by  the  connective  tissue.  They  do  not  penetrate 
into  the  cells,  but  each  cell  is  bathed  in  lymph  which  exudes  from 
the  blood-vessels.  One  of  the  substances  brought  by  the  blood 
to  the  muscles  is  glycogen.1  This  is  stored  in  the  cells  and  rep- 
resents potential  energy,  which  stimuli  may  transform  into  me- 
chanical energy.  The  transformation  of  energy  which  accom- 
panies muscular  activity  is  associated  with  the  oxidation  of  gly- 
cogen and  perhaps  fat,  and  the  formation  of  waste  compounds, 
i.e.,  carbon  dioxide,  water,  and  lactic  acid.  These  waste  com- 
pounds must  be  eliminated,  and,  except  in  cases  of  prolonged  con- 
tractions, the  system  is  able  to  get  rid  of  them  readily. 

Fatigue.  —  Prolonged  contractions  result  in  fatigue,  and  this 
means  two  things :  (1)  an  accumulation  of  waste  substances, 
which  act  as  poisons,  (2)  a  loss  of  nutrient  material.  A  period  of 
rest  furnishes  opportunity  for  the  blood  to  carry  these  fatigue  poi- 
sons to  the  excretory  organs;  and  nutritive  materials  from  the 
digestive  organs  to  the  muscles.  In  cases  of  extreme  fatigue 
resulting  from  prolonged  overwork  the  fatigue  poisons  circulate  in 
the  blood  and  lessen  the  irritability  of  muscular  tissue  so  that  it 
fails  to  respond  to  stimuli.  It  has  been  demonstrated  that  the 
injection  of  the  blood  of  a  fatigued  animal  into  a  rested  one  will 
promptly  bring  on  signs  of  fatigue. 

FUNCTIONALLY  IMPORTANT  SKELETAL  MUSCLES 

The  skeletal  muscles  are  usually  called  by  their  Latin  names, 
and  it  is  helpful  to  understand  the  meaning  of  these  names,  as 
they  are  often  descriptive  of  some  distinctive  characteristic,  such 
as  their  form,  size,  attachment,  location,  function,  etc. 

The  majority  occur  in  pairs.  Only  a  few  are  single,  and  they  are 
located  about  the  median  line.  Muscles  may  be  classified  in 
several  ways.  The  most  helpful  way  is  to  classify  them  according 

i  See  Chapter  XVI. 


104 


ANATOMY  AND  PHYSIOLOGY       [CHAP.  VII 


to  their  location  and  function.  It  is  most  important  for  nurses 
to  know  in  a  general  way  the  location,  and  in  a  definite  way  the 
function  of  the  principal  muscles  of  the  body. 


CHIEF   MUSCLES   OF   HEAD,    FACE,    TONGUE,    AND    NECK 
Muscles  of  the  Head       Occipito-frontalis 


Muscles  of  the  Face 


Muscles  of  the  Tongue 


Orbital  Muscles 


Muscles  of  Mastication 


Muscles  of  Expression 

Genioglossus. 
Styloglossus. 


Four  recti. 

Two  oblique. 

Levator  palpebrae   su- 
perioris. 

Masseter. 

Temporal. 

Internal  pterygoid. 

External  pterygoid. 
f  Orbicularis  oris. 
\  Buccinator. 


Muscles  of  the  Neck    I* 

[  feterno-cleido-mastoid. 

Muscles  of  the  head.  —  The  chief  muscle  of  the  head  is  the 
occipito-frontalis,  which  may  be  considered  as  two  muscles  united 
together  by  a  thin  aponeurosis  extending  over  and  covering  the 
whole  of  the  upper  part  of  the  cranium.  The  occipital  takes  its 
origin  from  the  occipital  bone  and  is  inserted  into  the  aponeurosis. 
The  frontal  takes  its  origin  from  the  tissues  in  the  region  of  the 
eyebrows,  and  is  also  inserted  into  the  aponeurosis. 

Action.  —  The  frontal  portion  of  this  muscle  is  the  more  power- 
ful ;  by  its  contraction  the  eyebrows  are  elevated,  and  the  skin  of 
the  forehead  thrown  into  transverse  wrinkles. 

Muscles  of  the  face.  —  There  are  about  thirty  facial  muscles ; 
they  are  chiefly  small,  and  only  a  few  are  considered.  We  group 
them  as :  (1)  Orbital  muscles,  (2)  Muscles  of  mastication,  and 
(3)  Muscles  of  expression. 

Orbital  muscles.  —  The  orbit  contains  seven  muscles ;  six  of 
them  are  attached  to  the  eyeball,  and  the  seventh  is  attached  to 
the  upper  lid.  The  six  muscles  attached  to  the  eyeball  are  arranged 
in  three  opposing  pairs. 

The  superior  and  inferior  recti. — These  two  muscles  have  their 
origin  at  the  apex  of  the  orbital  cavity  and  pass  straight  forward 


CHAP.  VII] 


SKELETAL   MUSCLES 


105 


to  their  insertion  into  the  eyeball,  the  superior  rectus  in  the  middle 
line  above,  and  the  inferior  rectus  opposite  it  below. 

Action.  —  Contraction  of  the    superior    rectus    rolls    the  eye 
upward ;   contraction  of  the  inferior  rolls  the  eye  downward. 


FIG.  72.  —  SUPERFICIAL  MUSCLES  OF  HEAD  AND  NECK.     (Gerrish.) 

The  internal  and  external  recti. — These  two  muscles  have  their 
origin  at  the  apex  of  the  orbital  cavity,  and  pass  forward  to  their 
insertion  into  the  eyeball ;  the  internal  on  the  inner  side,  the  ex- 
ternal on  the  outer  side. 


106 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  VII 


Action.  —  Contraction  of  the  internal  rectus  draws  the  eye 
inward  towards  the  nose.  Contraction  of  the  external  rectus 
draws  the  eye  outward. 


EXTERNAL 


y  " 


SUPERIOR  OBLIQUE 
SUPERIOR  RECTUS 


INTERNAL  RECTUS 


INFERIOR    RECTUS 
INFERIOR  O8LJQ.UE 


FIG.  73.  —  MUSCLES  OF  THE  RIGHT  EYEBALL  WITHIN  THE   ORBIT.     (Seen  from 

the  front.) 

Superior  oblique. — The  superior  oblique  muscle  arises  from  the 
apex  of  the  orbit  (the  same  as  the  four  recti),  courses  forward  to 
the  upper  and  inner  angle  of  the  orbit,  where  it  passes  through  a 


ELEVATOR   MUSCLE 
OF  THE  EYELID 


SUPERIOR  OBLIQUE 
SUPERIOR  RECTUS 

EXTERNAL  RECTUS 

INFERIOR   OBLIQUE 
INFERIOR   RECTUS 


FIG.  74.  —  Muscles  of  the  Eyeball.     (Seen  from  side.) 

loop  of  cartilage.  Then  it  bends  at  an  actue  angle,  passes  around 
the  upper  part  of  the  eyeball,  and  is  inserted  between  the  superior 
and  external  recti. 


CHAP.  VII] 


SKELETAL  MUSCLES 


107 


Inferior  oblique.  — -  The  inferior  oblique  arises  from  the  orbital 
plate  of  the  maxilla,  and  courses  around  the  under  portion  of  the 
eyeball  to  its  attachment  near  the  external  rectus. 


FIG.  75.  —  TEMPORAL  AND  DEEP  MUSCLES  ABOUT  THE  MOUTH.     (Gerrish.) 

Action.  —  The  action  of  the  two  oblique  muscles  is  somewhat 
complicated,  but  their  general  tendency  is  to  roll  the  eyeball  on  its 
axis. 

In  most  cases  the  movements  of  the  eye  are  somewhat  complex 
and  more  than  one  muscle  is  involved. 


108 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  VII 


Levator  palpebm  superioris  (lifter  of  the  upper  lid) .  —  It  arises 
from  the  sphenoid  bone,  passes  forward,  and  is  inserted  into  the 
tarsal  cartilage  of  the  upper  lid. 

Action.  —  It  elevates  the  upper  lid  and  opens  the  eye. 

Muscles  of  mastication.  —  They  are :  (1)  the  masseter  (chew- 
ing muscle),  (2)  the  temporal  (temple  muscle),  (3)  the  internal 


INFERIOR 
TURBINATEO 

BONE 


FIG.  76.  —  PTERYGOID  MUSCLES.     Viewed  from  behind,  the  back  portion  of  the 
skull  having  been  removed.      (Gerrish.) 

pterygoid,  and  (4)  the  external  pterygoid.  These  muscles  can 
be  located  on  the  illustrations.  They  have  their  origin  in  one  or 
more  of  the  immovable  bones  of  the  skull,  and  are  inserted  into 
the  movable  lower  jaw. 

Action.  —  (1)  The  masseter  raises  the  mandible.  (2)  The 
temporal  raises  the  mandible,  and  the  most  posterior  fibres  serve 
to  retract  the  jaw.  (3)  The  chief  action  of  the  internal  pterygoid 
is  to  raise  the  jaw ;  it  also  assists  the  external  pterygoid  in  pro- 


CHAP.  VII]  SKELETAL   MUSCLES  109 

trading  the  jaw  and  in  producing  lateral  movements.  (4)  When 
both  external  pterygoid  muscles  act  together  they  draw  the  jaw 
forward.  The  internal  and  external  pterygoid  of  one  side  pro- 
duce lateral  movements  of  the  jaw. 

These  muscles  generally  act  in  concert,  bringing  the  lower  teeth 
forcibly  into  contact  with  the  upper;  they  also  move  the  lower 
jaw  forward  upon  the  upper,  and  in  every  direction  necessary 
to  the  process  of  grinding  the  food. 

Muscles  of  expression.  —  These  muscles  are  sometimes  called 
mind  muscles  from  the  indications  that  they  afford  of  the  mental 
state  of  the  individual.  They  are  closely  connected  with  the 
under  surface  of  the  skin  or  with  each  other,  and  therefore  their 
slightest  contraction  is  shown  on  the  face.  They  include  the 
muscles  of  the  forehead,  eyelids,  nose,  and  all  those  related  to 
the  orifice  of  the  mouth.  We  shall  only  consider  two  important 
muscles  related  to  the  orifice  of  the  mouth. 

Orbicularis  oris. — The  ring  muscle  surrounds  the  opening  of 
the  mouth,  extending  from  the  nose  above  to  the  chin  below. 
It  forms  a  great  part  of  the  bulk  of  the  lips,  and  constitutes  a 
sphincter  to  the  mouth.  It  is  attached  above  to  the  partition 
between  the  nostrils  and  the  upper  jaw  bones,  and  below  to  the 
mandible. 

Action.  —  It  causes  compression  and  closure  of  the  lips  in  vari- 
ous ways,  e.g.,  tightening  the  lips  over  the  teeth,  contracting 
them,  or  causing  pouting  or  protrusion  of  one  or  the  other. 

Buccinator  (trumpeter's  muscle).  —  This  muscle  arises  from 
the  alveolar  processes  of  the  maxilla  and  mandible.  Its  different 
parts  converge  to  the  angle  of  the  mouth,  and  are  inserted  into  the 
orbicularis  oris. 

Action.  —  It  retracts  the  angles  of  the  mouth,  flattens  the 
cheeks,  and  brings  them  in  contact  with  the  teeth. 

Chief  muscles  of  the  tongue.  — The  chief  muscles  connecting 
the  tongue  and  hyoid  bone  to  the  lower  jaw  are  the  genioglossus 
and  the  styloglossus. 

Genioglossus.  —  The  genioglossus  has  its  origin  in  the  front  part 
of  the  mandible,  and  is  inserted  in  the  whole  length  of  the  tongue 
in  and  at  the  side  of  the  midline. 

Action.  —  It  thrusts  the  tongue  forward,  retracts  it,  and  also 
depresses  it. 


110  ANATOMY  AND   PHYSIOLOGY      [CHAP.  VII 

Styloglossus.  —  The  styloglossus  has  its  origin  in  the  styloid 
process  of  the  temporal  bone,  and  is  inserted  in  the  whole  length 
of  the  side  and  under  part  of  the  tongue. 

Action.  —  It  retracts  the  tongue  and  depresses  it. 

These  muscles  are  interesting  to  us  from  the  fact  that  during 
general  anaesthesia  they,  together  with  the  other  muscles,  become 


OR 
STVLOHYOID 


FIG.  77.  —  MUSCLES  OF  THE  TONGUE.     Viewed  from  the  right  side.     (Gerrish.) 

relaxed,  and  it  is  necessary  to  press  the  angle  of  the  lower  jaw 
upward  and  forward  in  order  to  prevent  the  tongue  from  falling 
backward  and  obstructing  the  larynx. 

Muscles  of  the  neck.  —  The  two  superficial  muscles  of  the 
neck  are :  (1)  platysma,  (2)  sterno-cleido-mastoid. 

Platysma  (broad  sheet  muscle) .  —  It  arises  from  the  skin  and 
areolar  tissue  covering  the  pectoral,  deltoid,  and  trapezius  muscles, 
and  is  inserted  in  the  mandible  and  muscles  about  the  angle  of 
the  mouth. 

Action.  —  It  depresses  the  mandible,  and  laterally  flexes  the 
head.  It  also  wrinkles  the  skin  of  the  side  of  the  neck. 

Sterno-cleido-mastoid. — The  most  prominent  muscle  of  the 
neck  is  the  sterno-cleido-mastoid.  It  is  named  from  its  origin 
and  insertion,  arising  from  part  of  the  sternum  and  clavicle,  and 


CHAP.  VII]  SKELETAL   MUSCLES  111 

being  inserted  into  the  mastoid  portion  of  the  temporal  bone. 
This  muscle  is  easily  recognized  in  thin  persons  by  its  forming 
a  cord-like  prominence  obliquely  situated  along  each  side  of 
the  neck. 

Action.  —  When  one  muscle  acts  alone,  it  flexes  the  head 
laterally,  and  rotates  it  to  the  opposite  side.  Both  muscles  acting 
together  (1)  flex  the  head  in  a  forward  direction,  and  (2)  serve  as 
extraordinary  muscles  .of  inspiration,  by  raising  the  sternum  and 
clavicles.  If  one  of  these  muscles  be  either  abnormally  con- 
tracted or  paralyzed,  we  get  the  deformity  called  Torticollis  or 
wry  neck. 

CHIEF  MUSCLES  OF  THE  TRUNK 
They  may  be  arranged  in  four  groups :  - 

f  Trapezius. 

1.  Muscles  of  the  Back  <  Latissimus  dorsi. 

[Erector  spinse  (Sacrospinalis) . 
f  Pectoralis  major. 

2.  Muscles  of  the  Chest         <  Pectoralis  minor. 

[  Serratus  magnus  (Serratus  anterior). 
f  External  intercostals. 

3.  Muscles  of  the  Thorax       |  Internal  intercostals. 

Levatores  costarum. 
External  oblique. 
Internal  oblique. 


4.  Muscles  of  the  Abdomen 


Rectus  abdominis. 
Trans  versalis. 
Quadratus  Lumborum. 


Muscles  of  the  back.  —  The  muscles  of  the  back  are  disposed 
in  five  layers,  one  beneath  another.  Our  list  includes  only  the 
two  large  muscles,  trapezius  and  latissimus  dorsi,  which  form  the 
superficial  layer,  and  the  erector  spinse,  which  forms  the  fourth 
layer. 

Trapezium.  —  The  trapezius,  so  called  because  right  and  left 
together  make  a  large  diamond-shaped  sheet,  arises  from  the 
middle  of  the  occipital  bone,  from  all  the  cervical  and  all  the 
thoracic  vertebrae.  The  connection  with  the  cervical  vertebras 
is  through  the  medium  of  the  ligamentum  nuchce,  which  is  a  form 
of  ligament  that  stretches  from  the  protuberance  of  the  occiput  to 
the  spinous  processes  of  the  seven  cervical  vertebrae.  (See  Fig. 


112 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  VII 


78.)  From  this  extended  line  of  origin  the  fibres  converge  to  their 
insertion  in  the  clavicle,  the  acromion  process,  and  the  spine  of 
the  scapula.  It  is  a  very  large  muscle,  and  covers  the  other  mus- 
cles of  the  upper  part  of  the  back  and  neck,  also  the  upper  portion 

of  the  latissimus  dorsi. 

Action.  —  The  action  of  the 
trapezius  must  be  considered  in 
three  parts.  The  upper  fibres 
raise  the  shoulder,  the  middle 
fibres  adduct  the  scapula,  and 
the  lower  fibres  rotate  the 
lower  angle  of  the  scapula 
toward  the  median  line. 

Latissimus  dorsi.  -  The 
latissimus  dorsi  arises  from  the 
last  six  thoracic  vertebrae,  and 
through  the  medium  of  the  lum- 
bar aponeurosis,  from  the  lum- 
bar and  sacral  part  of  the  spine 
and  from  the  crest  of  the  ilium. 
It  covers  the  lower  part  of  the 
back.  The  fibres  pass  upward 
and  converge  into  a  thick,  nar- 
row band,  which  winds  around 
and  finally  terminates  in  a  flat 
tendon,  which  is  inserted  into  the  front  of  the  humerus  just  below 
its  head. 

Action.  —  It  draws  the  arm  to  the  side,  draws  it  downward 
and  backward,  and  rotates  the  humerus  inward. 

Erector  spince.  —  The  fourth  layer  of  the  muscles  of  the  back 
is  formed  by  the  erector  spinae  (sacrospinalis)  which  constitutes 
the  greater  part  of  the  long  rounded  mass  located  on  either 
side  of  the  series  of  vertebral  spinous  processes.  It  extends  from 
the  lower  and  back  part  of  the  sacrum,  the  back  portion  of  the  ilia 
and  the  spines  of  the  lumbar  vertebrae  to  the  cervical  vertebrae 
and  the  mastoid  processes  of  the  temporal  bones.  It  is  a  com- 
pound muscle  beginning  below  in  a  single  mass  which  soon  divides 
into  three  portions,  two  of  which,  the  outer  and  middle,  further 
subdivide  into  three  portions  as  follows :  - 


FIG.  78.  —  THE   LIGAMENTUM 
Seen  from  the  right  side.      (Gerrish.) 


CHAP.  VII] 


SKELETAL  MUSCLES 


113 


Erector 

Spinae 

(Sacrospinalis) 


Outer  Division :  — 

Ilio-costalis 

Accessorius  ad  iliocostalem 

Cervicalis  ascendens. 

Middle  Division :  — • 

Longissimus  dorsi 
Transversalis  cervicis 
Trachelo-mastoideus. 

Inner  Division :  — 

Spinalis  dorsi. 


OCCIPITALIS 


TERES  MINOR 


OBL1Q.EXT* 


LAST 

LUMBAR 
VERTEBRA 


FIG.  79.  —  MUSCLES  IN  THE  SUPERFICIAL  LAYER  OF  THE  BACK.     (Gerrish.) 

These  muscles  end  at  different  levels  by  a  series  of  steps,  as  it 
were.     As  the  muscle  climbs  up  the  back  it  does  not  relinquish 


116 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  VII 


FIG.  82.  —  SERRATUS  MAGNUS  OF  RIGHT  SIDE.      The  scapula   has  been  turned 
backward  and  drawn  outward.     (Gerrish.) 


INTERNAL 

INTERCOSTAL 

SEEN  THROUGH 

.ARTIFICIAL  GAP 

IN   EXTERNAL 


FIG.  83.  —  INTERCOSTAL  MUSCLES  IN  RIGHT  WALL  OF  THORAX.     (Gerrish.) 


CHAP.  VII]  SKELETAL   MUSCLES  117 

Intercostals.  —  The  intercostals  are  found  filling  the  spaces  be- 
tween the  ribs.  Each  muscle  consists  of  two  layers,  one  ex- 
ternal and  one  internal,  and  as  there  are  eleven  intercostal  spaces 
on  each  side,  and  two  muscles  in  each  space,  it  follows  there 
are  forty-four  intercostal  muscles.  The  fibres  of  these  muscles 
run  in  opposite  directions. 

External  intercostals. — The  external  fibres  arise  from  the 
lower  border  of  a  rib,  run  downward,  and  inward,  toward 
the  mid-line  and  are  inserted  into  the  upper  border  of  the  next 
lower  rib. 

Action.  —  They  pull  the  ribs  upward  and  outward,  thereby  in- 
creasing the  chest  cavity. 

Internal  intercostals. — The  internal  fibres  arise  from  the  lower 
border  of  a  rib,  run  downward,  and  backward,  and  are  inserted 
into  the  upper  border  of  the  next  lower  rib. 

Action.  —  It  is  considered  probable  that  the  internal  inter- 
costals act  in  the  same  way  as  the  external,  although  some  au- 
thorities state  that  the  internal  muscles  depress  the  ribs. 

Levatores  costarum  (lifters  of  the  ribs). — The  levatores  cos- 
tarum  are  twelve  small  slips  that  arise  from  the  transverse  pro- 
cesses of  the  vertebrae  from  the  seventh  cervical  to  the  eleventh 
thoracic.  Each  one  spreads  out  in  a  fan-like  manner  as  it  de- 
scends to  its  insertion  in  the  rib  below. 

Action.  —  They  assist  in  elevating  all  the  ribs  and  with  other 
muscles  draw  the  lower  ribs  backward. 

Diaphragm.  —  The  diaphragm  is  a  thin,  musculo-fibrous  par- 
tition which  divides  the  ventral  cavity  of  the  body  into  thoracic 
and  abdominal  cavities.  It  is  irregularly  dome  shaped,  its  centre 
being  made  of  a  central  aponeurotic  tendon,  to  the  edges  of  which 
muscular  tissue  is  attached  which  radiates  to  the  circumference 
of  the  thorax  where  it  is  fastened  to  the  body  wall.  It  has  three 
large  openings :  for  the  passage  of  the  aorta,  the  largest  artery  of 
the  body ;  the  inferior  vena  cava,  one  of  the  largest  veins  of  the 
body;  and  the  oesophagus,  or  gullet;  it  has  also  some  smaller 
openings  for  the  passage  of  blood-vessels,  nerves,  etc.  The  upper 
or  thoracic  surface  of  the  diaphragm  is  highly  arched ;  the  heart 
is  supported  by  the  central  tendinous  portion  of  the  arch,  the 
right  and  left  lungs  by  the  lateral  portions,  the  right  portion  of 
the  arch  being  slightly  higher  than  the  left.  The  lower  or  under 


118 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  V1J 


surface  of  the  diaphragm  is  deeply  concave,  and  covers  the  liver, 
stomach,  pancreas,  spleen,  and  kidneys. 

Action.  —  The  diaphragm  is  probably  the  most  important 
voluntary  muscle  in  the  body,  as  well  as  the  chief  respiratory  and 
expulsive  muscle.  In  the  act  of  inspiration  the  diaphragm  con- 
tracts, and  in  contracting  flattens  out  and  descends,  the  abdominal 
viscera  are  pressed  downward,  and  the  thorax  is  expanded  verti- 


FIG.  84.  —  DIAPHRAGM.  Viewed  from  in  front.  (Gerrish.)  At  A  the  liver 
and  at  B  the  cardiac  end  of  the  stomach  are  underneath  the  diaphragm  and  push 
it  up  ;  at  C  the  tip  of  the  heart  pushes  the  diaphragm  down. 


cally.  In  forcible  acts  of  expiration,  and  in  efforts  of  expulsion 
from  the  thoracic  and  abdominal  cavities,  the  diaphragm  and  all 
the  other  muscles  which  tend  to  depress  the  ribs,  and  those  which 
compress  the  abdominal  cavity,  concur  in  powerful  action  to  empty 
the  lungs,  to  fix  the  trunk,  and  to  expel  the  contents  of  the  ab- 
dominal viscera.  Thus  it  follows  that  the  action  of  the  diaphragm 
is  of  assistance  in  expelling  the  foe'tus  from  the  uterus,  the  feces 
from  the  rectum,  the  urine  from  the  bladder,  and  its  contents 
from  the  stomach  in  vomiting. 


CHAP.  VII] 


SKELETAL   MUSCLES 


119 


Muscles  of  the  abdomen.  —  The  chief  muscles  of  the  abdomen 
are  :  (1)  external  oblique,  (2)  internal  oblique,  (3)  rectus  abdominis, 
(4)  transversalis,  and  (5)  quadratus  lumborum.  Of  these  muscles, 
the  rectus  is  in  front,  the  quadratus  is  behind,  and  the  contractile 
portion  of  the  obliquus  externus,  ob- 
liquus  internus,  and  transversalis  are  at 
the  side. 

External  oblique. — The  strongest  and 
most  superficial  of  the  abdominal  muscles 
is  the  external  oblique.  It  arises  from 
the  outer  surface  of  the  eight  lower  ribs. 
The  fibres  incline  downward  and  forward 
and  terminate  in  the  broad  aponeurosis, 
which,  meeting  its  fellow  of  the  opposite 
side  in  the  linea  alba,  covers  the  whole 
of  the  front  of  the  abdomen.  The 
lowest  fibres  of  the  aponeurosis  are 
gathered  together  in  the  shape  of  a 
thickened  band,  which  extends  from  the 
anterior  superior  spinous  process  of  the 
ilium  to  the  pubic  bone,  and  forms 
the  well-known  and  important  land- 
mark, the  inguinal  ligament,  more  com- 
monly known  as  Poupart's  ligament 
from  the  anatomist  who  first  described  it. 

Internal  oblique.  —  The  internal  ob- 
lique muscle  lies  just  beneath  the 
external  oblique.  It  arises  from  the 
inguinal  ligament,  the  outer  crest  of 
the  ilium,  and  slightly  from  the  lumbar  fascia.1  Its  most  pos- 
terior fibres  run  upward  and  forward  and  are  inserted  in  the 
costal  cartilages  of  the  four  lower  ribs.  At  the  outer  border  of 
the  rectus  muscle  the  remaining  muscle  fibres  expand  into  a 
broad  aponeurosis.  This  aponeurosis  divides  into  two  layers,  one 
passing  before,  the  other  behind,  the  rectus  muscle ;  they  reunite 
at  its  inner  border  in  the  linea  alba,  and  thus  form  a  sheath  for 
the  rectus,  extending  from  the  xiphoid  process  to  the  crest  of 


FIG.  85.  —  RECTUS  ABDOM- 
INIS AND  OBLIQUUS  INTERNUS 
OF  RIGHT  SIDE.  (Gerrish.) 


1  The  lumbar  fascia  springs  from  the  lumbar  and  sacral  portions  of  the  vertebral 
column,  in  three  layers. 


120 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  VII 


the  pubes.     At  the  lower  part  of  the  rectus  the  posterior  layer 
of  the  aponeurosis  is  deficient. 

Rectus  abdominus.  —  The  rectus  is  a  long,  flat  muscle,  consisting 
of  vertical  fibres  situated  at  the  fore  part  of  the  abdomen,  and 
enclosed  in  the  fibrous  sheath  formed  by  the  aponeuroses  of  the 

internal  oblique,  the  external  oblique, 
and  the  transversalis  muscles.  It  arises 
from  the  pubic  bone,  and  is  inserted  into 
the  cartilages  of  the  fifth,  sixth,  and 
seventh  ribs ;  it  is  separated  from  the 
muscle  of  the  other  side  by  a  narrow 
interval  which  is  occupied  by  the  linea 
alba. 

Transversalis.  -  -  The  transversalis 
muscle  lies  beneath  the  internal  oblique. 
The  fibres  arise  from  the  six  lower  costal 
cartilages,  the  lumbar  fascia,  the  crest 
of  the  ilium,  and  the  outer  third  of  the 
inguinal  ligament.  The  greater  part  of 
its  fibres  have  a  horizontal  direction, 
and  are  inserted  in  the  linea  alba  and 
the  crest  of  the  pubes. 

Linea  alba.  —  The  linea  alba,  or  white 
line,  is  a  tendinous  band  formed  by  the 
union  of  the  aponeuroses  of  the  two  ob- 
lique and  transversalis  muscles,  the  ten- 
dinous fibres  crossing  one  another  from 
side  to  side.  It  extends  perpendicularly, 
in  the  middle  line,  from  the  xiphoid 
portion  of  the  sternum  to  the  pubes. 
It  is  a  little  broader  above  than  below,  and  a  little  below  the 
middle  it  is  widened  into  a  flat,  circular  space,  in  the  centre  of 
which  is  situated  the  umbilicus. 

Quadratus  lumborum.  —  The  quadratus  lumborum  is  a  square, 
flat  muscle  which  lies  toward  the  back  part  of  the  abdominal  wall, 
extending  between  the  crest  of  the  ilium  and  the  lower  border  of 
the  twelfth  rib.  (See  Fig.  90.) 

Action  of  the  abdominal  muscles.  —  When  these  muscles  con- 
tract, they  compress  the  abdominal  viscera,  and  constrict  the 


FIG.  86.  —  TRANSVERSALIS 
ABDOMINIS  OF  RIGHT  SIDE. 
(Gerrish.) 


CHAP.  VII]  SKELETAL  MUSCLES  121 

cavity  of  the  abdomen,  in  which  action  they  are  much  assisted  by 
the  descent  of  the  diaphragm.  By  these  means  they  give  assist- 
ance in  parturition,  defecation,  micturition,  and  emesis.  They 
also  assist  in  respiration,  flex  the  thorax  on  the  pelvis,  and  are 
concerned  with  lateral  bending  and  rotation  at  the  spine. 

The  inguinal  canal.  —  Between  the  abdominal  muscles,  parallel 
to,  and  about  one-half  inch  above  the  inguinal  ligament,  is  a  tiny 
canal,  about  one  and  one-half  inches  long,  called  the  inguinal  canal. 
The  internal  opening  of  the  canal  is  called  the  internal  abdominal 
ring,  and  is  situated  in  the  fascia  of  the  transversalis  muscle,  mid- 
way between  the  spine  of  the  ilium  and  the  crest  of  the  pubic  bone. 
The  canal  ends  in  the  external  abdominal  ring,  which  is  in  the 
tendon  of  the  external  oblique  muscle.  This  canal  transmits  the 
spermatic  cord  in  the  male,  and  the  round  ligament  of  the  uterus 
in  the  female. 

Weak  places  in  the  abdominal  walls.  —  The  internal  and  ex- 
ternal abdominal  rings,  described  above,  the  umbilicus,  and  an- 
other ring  situated  just  below  the  inguinal  ligament,  and  called  the 
femoral  ring,  are  considered  weak  places  because  they  are  so  often 
the  seat  of  hernia.  Hernia,1  or  rupture,  is  a  protrusion  of  a  portion 
of  the  contents  of  a  body  cavity,  and  in  this  instance  would  mean 
a  protrusion  of  a  portion  of  the  intestine  or  mesentery  through  one 
of  these  weak  places.  If  it  occurs  in  the  umbilicus,  it  is  called 
umbilical  hernia;  in  the  inguinal  rings,  inguinal  hernia;  and  in  the 
femoral  ring,  femoral  hernia.  The  inguinal  canal  is  larger  in  the 
male  than  in  the  female,  hence  inguinal  hernia  is  more  common 
in  the  male  than  in  the  female. 

MUSCLES  OF  THE  UPPER  EXTREMITIES 

A  certain  number  of  muscles  situated  superficially  on  the  trunk 
are  frequently  grouped  with  the  muscles  of  the  upper  extremities, 
as  their  function  is  to  attach  the  upper  limbs  to  the  trunk  and 
move  the  shoulders  and  arms.  Of  these,  the  two  superficial 
muscles  we  have  mentioned  as  covering  the  back,  and  the  muscles 
covering  the  front  of  the  chest,  are  the  chief. 

The  muscles  of  the  extremities  are  arranged  in  antagonistic 

1  If  the  skull  is  injured  so  that  a  portion  of  the  brain  protrudes,  it  would  also 
be  correctly  spoken  of  as  hernia  of  the  brain.  Of  course  this  is  more  unusual  than 
abdominal  hernia. 


122 


ANATOMY  AND   PHYSIOLOGY     .[CHAP.  VII 


groups,  the  action  of  one  group  opposing  the  action  of  the  other. 
The  movements  of  which  the  extremities  are  capable  are  flexion 
and  extension,  abduction  and  adduction,  supination  and  prona- 
tion,  circumduction  and  rotation.  (See  page  94.) 

Functionally  we  may  group  the  muscles  of  the  upper  extremi- 
ties as  follows :  — 


NAME  op 
MUSCLE 

LOCATION 

FUNCTION 

Trapezius 

Upper  portion  of 

Moves     shoulder    upward, 

back 

backward,  and   inwardly 

, 

rotates  the  scapula. 

Moving  the 
Shoulder 

Pectoralis 
minor 

Chest,  under 
pectoralis 

Moves    shoulder    forward, 
thus   assisting   action   of 

major 

serratus  magnus. 

Serratus 

Upper  two-thirds 

Moves     shoulder     forward 

magnus 

of  side  of  chest 

and     rotates     apex      of 

scapula  upward. 

Deltoid 

Covers  the  top  of 

Abduction,     forward     and 

the  shoulder 

backward  motion. 

Moving  the 
Arm 

Pectoralis 
major 

Chest,  from 
sternum  to 

Adduction,  forward  motion 
and  inward  rotation. 

r\L  ill 

humerus 

Latissimus 

Lower  portion  of 

Adduction,  and  rotates  the 

dorsi 

back 

humerus  inward. 

Biceps 

Anterior  surface 

Flexes  the  elbow  joint  and 

of  arm 

supinates  the  forearm. 

Triceps 

Posterior  surface 

Extension. 

Moving  the 

of  arm 

Forearm 

Pronators 

Anterior  surface 

Pronation. 

of  forearm 

Supinators 

Posterior  surface 

Supination 

of  forearm 

Deltoid.  —  The  deltoid  is  a  coarse,  triangular  muscle  covering 
the  top  of  the  shoulder.  It  arises  from  the  clavicle,  acromion 
process,  and  spine  of  the  scapula,  extends  downward,  and  is  in- 
serted into  the  middle  of  the  shaft  of  the  humerus,  on  the  outer 
side.  (See  Fig.  81.) 

Action.  —  It  abducts  —  raises  the  arm  from  the  side  so  as  to 
bring  it  at  right  angles  to  the  trunk,  also  draws  the  arm  forward 


CHAP.  VII] 


SKELETAL   MUSCLES 


123 


and  backward.     This  action  is  opposed  by  the  pectoralis  major 
and  the  latissimus  dorsi,  which  have  been  described. 

Biceps.  —  The  biceps  is  a  long  fusiform  muscle,  occupying  the 
whole  of  the  anterior  surface  of  the  arm ;  it  is  divided  above 
into  two  portions  or  heads,  from  which  circumstance  it  has  re- 


FIG.  87.  —  MUSCLES  OF  THE 
FRONT  OF  THE  RIGHT  SHOULDER 
AND  ARM.  (Gerrish.) 


FIG.    88.  —  MUSCLES    ON    THE    DORSUM    OF    THE 
RIGHT  SHOULDER  AND  ARM.     (Gerrish.) 


ceived  its  name.  It  arises  by  these  two  heads  from  the  scapula, 
and  is  inserted  into  the  radius. 

Action.  —  The  action  of  the  biceps  is  complex,  as  it  affects 
three  joints.  The  muscle  raises  and  draws  forward  the  humerus 
at  the  shoulder  joint,  flexes  the  elbow  joint,  and  supinates  the  fore- 
arm. The  combination  of  these  movements  produces  a  simple 
act,  e.g.,  raising  the  hand  to  the  mouth. 

Triceps.  —  The  triceps  is  situated  on  the  back  of  the  arm, 
extending  the  whole  length  of  the  posterior  surface  of  the  humerus. 


124 


ANATOMY  AND  PHYSIOLOGY      [CHAP.  VII 


It  is  of  large  size,  and  divided  above  into  three  heads ;  hence  its 
name.     Two  of  the  heads  have  their  origin  in  the  scapula  and  one 

in  the  humerus.  The  three  heads  unite 
in  a  common  tendon  which  is  inserted 
into  the  ulna. 

Action.  —  It  is  the  great  extensor 
muscle  of  the  forearm,  and  is  the 
direct  antagonist  of  the  biceps. 

Muscles  of  the  forearm.  —  The 
muscles  covering  the  forearm  are  dis- 
posed in  groups,  the  pronators  and 
flexors  being  placed  on  the  front  and 
inner  part  of  the  forearm,  and  the 
supinators  and  extensors  on  the  outer 
side  and  back  of  the  forearm  :  they  an- 
tagonize one  another.  The  pronators 
turn  the  palm  of  the  hand  backward 
and,  when  the  elbow  is  flexed,  down- 
ward or  prone.  The  supinators  turn 
the  palm  of  the  hand  forward,  and, 
when  the  elbow  is  flexed,  upward  or 
into  the  supine  position.  The  flexors 
and  extensors  have  long  tendons,  some 
of  which  are  inserted  into  the  bones  of 
the  wrist,  and  some  into  the  bones  of 
the  fingers :  they  serve  to  flex  and 
extend  the  wrist  and  fingers. 

MUSCLES   OF  THE   LOWER  EX- 
TREMITIES 

If  we  compare  the  muscles  of  the 
shoulder,  arm,  and  forearm  with  those 
of  the  hip,  thigh,  and  leg,  we  shall  see 
that  the  anterior  muscles  of  the  former 
correspond  roughly  with  the  posterior  muscles  of  the  latter,  the 
muscles  of  the  hip,  thigh,  and  leg,  however,  being  larger  and 
coarser  in  texture  than  those  of  the  shoulder,  arm,  and  forearm. 
Functionally  we  may  group  the  most  important  muscles  of 
the  lower  extremities  as  follows :  — 


ANNULAR 
LIGAMENT 


FIG.  89.  —  MUSCLES  IN  THE 
DORSUM  OF  THE  RlGHT  FORE- 
ARM  AND  HAND.  (Gerrish.) 


CHAP.  VII] 


SKELETAL   MUSCLES 


125 


NAME  op  MUSCLE 

LOCATION 

FUNCTION 

Psoas  magnus 

In  the  pelvis 

(Flexion,  outward  rota- 

Iliacus 

and    upper 

tion  and,  according  to 

part  of 

some  authors,  inward 

thigh 

rotation. 

Gluteus  maximus 

Region  of  but- 

Extension, outward  ro- 

tocks 

tation  and  adduction.* 

Gluteus  medius 

Under  gluteus 

f  Abduction 

Moving 

maximus 

and 

the 

Gluteus  minimus 

Under  gluteue 

inward 

Thigh 

medius 

rotation. 

Adductor  magnus 

' 

Adductor    and    extensor 

Adductor    longus 

Adducts  and  assists  in 

Adductor    brevis 

Mesial     part 

flexing  the  thigh 
Addicts  and  flexes  the 

of  thigh 

thigh. 

Adductor  gracilis 

Adducts  thigh  and  flexes 

the  leg. 

Sartorius 

Front  of 

Flexes  the  hip  and  knee 

thigh 

joints,    everts   thigh, 

and   assists   in   rota- 

tion of  tibia. 

Biceps 

i 

• 

Moving 

Semitendinosus 

Back  of 

Flexors  of  knee,  rotate' 

the 

Semimembra- 

thigh 

leg,  and  extend  thigh. 

Leg 

nosus 

a 

Rectus  femoris 

Vastus  externus 
Vastus  interims 
Vastus  inter- 

£ 
Front  of 

thigh 

t> 

Extension  of  leg,  flexes 
the  thigh 

medius 

Of 

Tibialis  anterior 
Peroneus  tertius 

Front  of  leg 

1  Flexes  the  ankle 

Moving 
the 
Foot 

Tibialis  posterior 
Gastrocnemius 

Back  of  leg 

f  Extensor  of  ankle 
1  Flexes  knee  and  extends 
ankle 

Soleus 

[  Extensor  of  ankle 

Peroneus.  longus 
Peroneus  brevis 

Outer  part  of 
leg 

|  Extensors 

Psoas  magnus.  —  The  great  loin  muscle  arises  from   the   last 
thoracic  and  all  the  lumbar  vertebrae  with  the  included  inter- 


126 


ANATOMY  AND  PHYSIOLOGY       [CHAP.  VII 


vertebral  cartilages.  It  extends  downward  and  forward,  then 
downward  and  backward,  to  its  insertion  in  the  small  trochanter 
of  the  femur. 


FIG.  90.  —  PSOAS,  ILIACUS,  AND  OBTURATOR  EXTERNUS  MUSCLES.     (Gerrish.) 

Iliacus.  —  This  muscle  and  its  relation  to  the  psoas  magnus  is 
well  shown  in  Fig.  90.  It  arises  from  the  iliac  fossa  and  is  inserted 
partly  into  the  tendon  of  the  psoas  and  partly  into  the  small 
trochanter  of  the  femur. 

Action.  —  The  psoas  magnus  and  iliacus  act  as  one  muscle  to 
flex  the  thigh  on  the  pelvis,  and  rotate  the  femur  outward  or  ac- 
cording to  some  authors,  inward. 


CHAP.  VII] 


SKELETAL  MUSCLES 


127 


FIG.  91. —  GLUTEUS  MAXIMUS  OF  RIGHT 
SIDE.     (Gerrish.) 


Glutei  muscles.  —  The  three  gluteal  muscles  are  coarse  in  tex- 
ture, and  form  the  chief  prominence  of  the  buttocks. 

Glutens  maximus  arises  from 
the  ilium,  sacrum,  and  coccyx, 
and  is  inserted  into  the  great 
trochanter  of  the  femur. 

Action.  —  It  is  a  powerful 
extensor  of  the  hip-joint.  It 
also  rotates  the  femur  out- 
ward, and  adducts  the  thigh. 

Glutens  medius  and  glutens 
minimus  are  under  the  gluteus 
maximus  and  almost  entirely 
covered  by  it.  They  arise 
from  the  outer  surface  of  the 
ilium  and  are  inserted  into  the 
great  trochanter. 

Action.  —  Abduction  of  the 
thigh,  and  inward  rotation. 

Adductors.  —  The  four  ad- 
ductor muscles  are  called  respectively  magnus  (great),  longus 
(long) ,  brevis  (short) ,  and  gracilis  (slender) .  They  are  situated  on 
the  inner  side  of  the  thigh.  They  arise  from  different  portions  of 
the  pubic  bone,  and  the  first  three  are  inserted  into  the  inner 
side  of  the  femur.  The  gracilis  is  inserted  into  the  shaft  of 
the  tibia. 

Action.  —  The  magnus  adducts  and  extends  the  thigh ;  the 
longus  and  brevis  adduct  and  flex  the  thigh.  The  gracilis 
adducts  the  thigh  and  flexes  the  leg. 

Sartorius.  —  The  sartorius,  or  tailor's  muscle,  is  a  long,  ribbon- 
like  muscle  situated  on  the  front  of  the  thigh.  It  crosses  the  thigh 
obliquely  from  its  origin  in  the  ilium  to  its  insertion  in  the  tibia. 
It  was  formerly  supposed  to  be  the  muscle  principally  concerned 
in  producing  the  posture  assumed  by  the  tailor  in  sitting  cross- 
legged,  hence  its  name. 

Action.  —  It  flexes  the  hip  and  knee  joints,  everts  the  thigh, 
and  assists  in  rotation  of  the  tibia. 

Biceps.  —  The  biceps  arises  by  two  heads,  one  from  the  ischium, 
and  the  other  from  the  posterior  surface  of  the  femur.  It  is  in- 


128 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  VII 


serted  into  the  head  of  the  fibula  and  the  outer  tubercle  of  the 
tibia. 

Semitendinosu?    and     Semimembranosus.  —  They    arise    from 
the  ischium,  and  are  inserted  into  the  upper  and  inner  part  of 


FIG.  92.  —  MUSCLES  IN  THE 
DORSUM  OF  THE  RlGHT  THIGH. 
(Gerrish.) 


FIG.  93.  —  SUPERFICIAL 
FRONT   PART   OF   THE    RIGHT   THIGH. 

(Gerrish.) 


the  tibia.  These  three  muscles,  the  biceps,  semitendinosus,  and 
semimembranosus,  cover  the  back  of  the  thigh,  hence  are  named 
posterior  femoral,  or  hamstring  muscles. 


CHAP.  VII] 


SKELETAL   MUSCLES 


129 


Action.  —  They  flex  the  knee,  rotate  the  leg,  and  extend  the 
thigh. 

Quadriceps.  —  The  quadriceps  is  a  four-headed  muscle  that 
covers  the  front  of  the  thigh,  and  is  analogous  to  the  triceps  cover- 
ing the  back  of  the  arm.  Each  head  is 
described  as  a  separate  muscle :  (1)  rectus 
femoris,  (2)  vastus  externus,  (3)  vastus  in- 
ternus,  (4)  vastus  intermedius. 


I 


GA< 


FIG.    94.  —  VASTUS    INTERMEDIUS   OF   RIGHT    SIDE. 
(Gerrish.) 

The  rectus  femoris  arises  from  the  ilium, 
the  other  three  arise  from  the  femur. 
They  pass  downward,  and  are  inserted  by 
one  tendon  into  the  tubercle  of  the  tibia. 
The  tendon  passes  in  front  of  the  knee-joint,  and  the  patella  is  a 
sesamoid  bone  developed  in  it. 

Action.  —  The  quadriceps  is  the  great  extensor  of  the  leg ;    it 


FIG.  95.  —  GASTROC- 
NEMIUS  OF  RIGHT  SIDE. 
(Gerrish.) 


130  ANATOMY  AND   PHYSIOLOGY       [CHAP.  VII 

also  flexes  the  thigh,  and  antagonizes  the  action  of  the  hamstring 
muscles. 

Gastrocnemius  and  soleus.  —  The  gastrocnemius  and  soleus 
form  the  calf  of  the  leg.  The  gastrocnemius  arises  by  two  heads 
from  the  two  condyles  of  the  femur.  The  soleus  is  in  front  of  the 
gastrocnemius.  It  arises  from  the  tibia  and  fibula.  The  direc- 
tion of  both  is  downward,  and  they  are  inserted  into  a  common 
tendon,  the  tendon  of  the  heel  (tendo  Achillis),  which  is  the  thick- 
est and  strongest  tendon  in  the  body,  and  is  inserted  into  the  cal- 
caneum,  or  heel  bone. 

Action.  —  The  gastrocnemius  flexes  the  knee,  extends  the 
ankle,  and  is  responsible  for  the  spring  in  the  gait  at  the  end  of  a 
step.  The  muscle  is  a  powerful  one  and  should  be  capable  of  rais- 
ing about  twice  the  weight  of  the  body.  The  soleus  is  a  powerful 
extensor  of  the  ankle.1 

1  Additional  muscles  included  in  Summary. 


CHAP.  VII] 


SUMMARY 


131 


Muscular  tissue 


Classification 


Striated 


f  Voluntary 
Skeletal 


Non-       f  Involuntary 
striated  i  Visceral 


Cardiac 


Striated 

Involuntary 

Visceral 


Characteristics  of 
muscular  tissue 


Function   .     .     . 


SUMMARY 

Cells  become  elongated. 

Intercellular  substance  which  is  at  a  minimum. 
Connective  tissue  —  supporting  framework. 
Well  supplied  with  nerves  and  blood-vessels. 

1.  Striated,  voluntary,  skeletal. 

2.  Non-striated,  involuntary,  visceral. 

3.  Cardiac. 

1.  Marked  with  transverse  striae. 

2.  Under  control  of  will. 

3.  Attached  to  skeleton. 

4.  Composed  of  bundles  of  multinuclear  elon- 

gated cells. 

5.  Reticular  tissue  framework. 

6.  Attached  to  bones,  cartilage,  ligaments,  skin 

by  means  of  tendons. 

7.  One  muscle  connects  with  another  by  means 

of  an  aponeurosis. 

8.  Muscles  closely  covered  by  sheets  of  fascia. 

9.  Deep  fascise  form  annular  ligaments  in  vicin- 

ity of  wrist  and  ankle. 

10.  Origin  —  more  fixed  attachment. 

11.  Insertion  —  more  movable  attachment. 

1.  Not  marked  with  transverse  striae. 

2.  Not  under  control  of  will. 

3.  Found  in  walls  of  blood-vessels  and  viscera. 

4.  Composed  of  bundles  of  elongated  cells  that 

contain  just  one  nucleus. 

5.  Reticular  tissue  framework. 

1.  Striated  but  not  distinctly. 

2.  Not  under  control  of  will. 

3.  Made  up  of  short   cells,   that   contain  one 

nucleus,  no  sarcolemma. 

4.  Cells  grouped  in  square  bundles. 

5.  Fine  fibrils  from  cells  form  a  supporting  net- 

work. 

6.  Reticular  tissue  framework. 

1.  Irritability  —  response  to  a  stimulus. 

2.  Contractility  —  muscle  becomes  shorter  and 

thicker. 

3.  Extensibility  —  muscle  can  be  stretched. 

4.  Elasticity  —  muscle  readily  returns  to  original 

shape. 

5.  Tonicity  —  mild,  sustained  contraction. 
Contraction.     On  this  muscular  activity  depends. 


132 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  VII 


Stimuli 


Varieties  of  Muscular 
Movements 


Nerves 


Conditions     of     Con- 
traction 


Source  of  Energy    . 


Varieties 


Involuntary  —  automatic 
Cardiac         —  automatic 


Term  used  to  describe  influences  which  irritate 
or  stimulate. 

1.  Chemical. 

2.  Mechanical. 

3.  Thermal. 

4.  Electrical. 

5.  Nervous  —  important  one. 

Voluntary  —  stimuli  from  central  nervous  system. 

Stimuli  from  nervous 
system  increase  or 
decrease  activity. 

Afferent  —  Carry    impulses   from    periphery    to 

brain,  spinal  cord,  or  ganglia. 
Afferent  nerves  connected  with  mus- 
cles are  spoken  of  as  sensory. 
Efferent  —  Carry  impulses  to  the  periphery  from 

brain,  spinal  cord,  or  ganglia. 
Efferent  nerves  that  end  in  muscles 
are  spoken  of  as  motor. 

Skeletal  muscle  —  contracts      quickly,      relaxes 

promptly. 

Visceral  muscle  —  contracts  slowly,  maintained 
for  some  time,  fades  out 
slowly. 

Heart  muscle  —  contracts    and    relaxes    unceas- 
ingly during  life. 

'  Result  of  series  of  rhythmic  stimuli. 
Contrac-  Latent  period     .     .01  sec. 

tions    Consist  of     Contraction  period  .04  sec. 
Relaxation  period   .05  sec. 

Tetanus  —  compound  contraction,  due  to  stimuli 
being  received  too  rapidly  to  allow 
for  periods  of  relaxation. 

Well  supplied  with  blood  from  which  glycogen  is 

obtained  and  stored. 
Glycogen  represents  potential  energy. 
Stimuli  transform  potential  energy  to  mechanical 
energy. 

Oxidation  of  glycogen  and  perhaps  fat. 
Carbon  dioxide 


Chemical 
Change 


Waste  sub- 
stances 


Water 
Lactic  acid 


Fatigue      .     . 


Loss  of  nutritive  materials. 
Accumulation  of  waste  substances, 


CHAP.  VII] 


SUMMARY 


133 


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CHAPTER  VIII 

SPECIAL  MEMBRANES  AND  GLANDS 
MEMBRANE 

THE  word  membrane  in  its  widest  sense  is  used  to  designate 
any  thin  expansion  of  tissue.  In  a  restricted,  although  the  com- 
monest sense,  the  word  membrane  is  used  to  denote  an  envelop- 
ing or  a  lining  tissue  of  the  body. 

Classification  of  membranes.  —  The  chief  membranes  of  the 
body  are  classified  as  follows  :  — 

1.  Serous. 

2.  Sy  no  vial. 

3.  Mucous. 

4.  Cutaneous. 

SEROUS  MEMBRANES 

Serous  membranes  are  thin,  transparent,  tolerably  strong,  and 
elastic.  The  surfaces  are  moistened  by  a  fluid  resembling  serum, 
from  which  the  membranes  obtain  their  name  of  serous  mem- 
branes. They  are  found  lining  closed  cavities  and  passages  that 
do  not  communicate  with  the  exterior.  They  consist  of  two  layers 
only:  (1)  endothelium,  (2)  corium. 

(1)  Endothelium  is  the  name  given  to  a  variety  of  epithelium 
found  lining  (i.e.,  lying  within)  certain  parts  of  the  body.     It  con- 
sists of  a  single  layer  of  flattened  transparent  cells  joined  edge  to 
edge  so  as  to  form  a  smooth  membrane. 

(2)  The  corium  consists  of  a  thin  layer  of  fibrous  tissue,  and 
contains  blood-vessels,  lymph-vessels,  and  lymphoid  tissue. 

Serous  membranes  are  attached  to  the  underlying  parts  by 
areolar  tissue,  called  suhserous  tissue.  They  may  be  divided  into 
three  classes :  — 

(1)  Serous  membranes  proper. 

(2)  The  lining  membrane  of  the  vascular  system. 

(3)  The  lining  membrane  of  certain  cavities. 

140 


CHAP.  VIII]     SPECIAL  MEMBRANES  AND   GLANDS     141 

(1)  Serous  membranes  proper. — With  one  exception,  these 
membranes  form  closed  sacs,  one  part  of  which  is  attached  to  the 
walls  of  the  cavity  which  it  lines,  —  the  parietal  portion,  —  whilst 
the  other  is  reflected  over  the  surface  of  the  organ  or  organs  con- 
tained in  the  cavity,  and  is  named  the  visceral  portion  of  the  mem- 
brane.    In  this  way  the  viscera  are  not  contained  within  the  sac, 
but  are  really  placed  outside  of  it,  and  some  of  the  organs  may 
receive  a  complete,  while  others  receive  only  a  partial,  or  scanty, 
investment. 

This  class  of  serous  membranes  includes :  — 

(a)    The  two  pleura,  which  cover  the  lungs  and  line  the  chest. 

(6)  The  pericardium,  which  covers  the  heart,  and  lines  the 
outer  fibrous  pericardium. 

(c)  The  peritoneum,1  which  lines  the  abdominal  cavity,  clothes 
its  contained  viscera,  and  also  the  upper  surface  of  some  of  the 
pelvic  viscera. 

(2)  The  lining  membrane  of  the  vascular  system.  —  This  ap- 
plies to  the  internal  coat  of  the  heart,  blood-vessels,  and  lymphatics. 
It  bears  a  close  resemblance  to  the  serous  membranes  in  structure 
and  appearance. 

(3)  The  lining  membrane  of  certain  cavities  :  — 

(a)  One   illustration   of  this   is  the   capsule   of  Tenon.     This 
capsule  is  a  shut  sac  placed  back  of  the  eyeball,  with  a  visceral 
layer  upon  the  globe  of  the  eye,  and  the  parietal  layer  next  to  the 
bed  of  fat  on  which  the  eyeball  rests. 

(b)  The  brain  and  spinal  cord  enclose  cavities  which  are  lined 
with  a  delicate  serous  membrane.     One  of  the  membranes  that 
envelop  the  brain  and  spinal  cord  (arachnoid)  presents  all  the 
elements   of    a   serous   membrane,    and    is   properly    considered 
as  one. 

Function  of  serous  membranes.  —  The  most  important  function 
of  serous  membrane  is  protection,  which  is  accomplished  in  two 
ways  :  (1)  by  forming  a  smooth,  slippery  lining  or  covering  for  the 
blood-vessels,  cavities,  and  viscera  with  which  it  is  associated,  and 
(2)  by  secreting  serum  which  acts  as  a  lubricating  fluid  and  tends 
to  lessen  friction. 

1  The  peritoneum  in  the  female  is  the  one  exception  to  the  rule  that  serous  mem- 
branes are  perfectly  closed  sacs,  as  it  has  two  openings  by  which  the  Fallopian 
(uterine)  tubes  communicate  with  its  cavity. 


142 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  VIII 


The  inner  surface  of  a  serous  membrane  is  free,  smooth,  and 
polished ;  and  in  the  case  of  serous  membranes  proper,  the  inner 
surface  of  one  part  is  applied  to  the  corresponding  inner  surface  of 
some  other  part,  only  a  very  small  quantity  of  fluid  being  interposed 
between  the  surfaces.  The  organs  situated  in  a  cavity  lined  by  a 
serous  membrane,  being  themselves  also  covered  by  it,  can  thus 
glide  easily  against  its  walls  or  upon  each 
other,  their  motions  being  rendered  smoother 
by  the  lubricating  fluid. 


SYNOVIAL  MEMBRANES 

Synovial  membranes  are  frequently 
classed  as  serous  membranes,  because  their 
function  is  the  same  and  they  have  no 
communication  with  the  surface  of  the 
body.  They  differ,  however,  (1)  in  the 
nature  of  their  secretion,  (2)  in  their  struc- 
ture, and  (3)  they  are  associated  with  the 
bones  and  muscles,  and  not  with  the  viscera. 
Synovial  membrane  is  composed  of  fibrous 
tissue  which  has  on  its  free  surface  an  im- 
perfect covering  of  cells  that  are  irregularly 
shaped,  and  secrete  a  viscid  glairy  fluid 
that  resembles  the  white  of  egg,  and  is 
named  synovia. 

They    are    divided     into    the    following 

classes :  — 

1.  Articular. 

2.  Vaginal. 

3.  Bursal. 


FIG.  96.  —  THE  AN- 
TERIOR ANNULAR  LIGA- 
MENT OF  THE  ANKLE 
AND  THE  SYNOVIAL  MEM- 
BRANES OF  THE  TENDONS 
BENEATH  IT.  Artificially 
(Gerrish.) 


distended. 


1.  Articular.  —  Articular  synovia!  mem- 
branes are  found  surrounding  and  lubri- 
cating the  cavities  of  the  movable  joints  in  which  the  opposed 
surfaces  glide  on  each  other.1 

2.  Vaginal.  —  Vaginal  synovial  membranes  are  found  forming 
sheaths  for  the  tendons  of  some  of  the  joints,  and  thus  facilitating 
their  motion  as  they  glide  in  these  fibrous  sheaths  which  bind  them 
down  against  the  bones. 

1  See  Fig.  69. 


CHAP.  VIII]     SPECIAL  MEMBRANES  AND   GLANDS     143 

3.  Bursal.  —  Bursal  synovial  membranes,  or  synovial  bursse, 
are  found  in  the  form  of  simple  sacs,  interposed,  to  prevent 
friction,  between  two  surfaces  which  move  upon  each  other. 
These  bursse  may  be  either  deep-seated,  or  Subcutaneous.  The 
deep-seated  are  for  the  most  part  placed  between  a  muscle  and  a 
bone,  or  between  a  tendon  and  a  bone.  The  subcutaneous  bursse 
lie  immediately  under  the  skin,  and  occur  in  various  parts  of 
the  body,  interposed  between  the  skin  and  some  firm  prominence 
beneath  it.  The  large  bursa,  situated  over  the  patella,  is  a  well- 
known  example  of  this  class,  but  similar,  though  smaller,  bursse 
are  found  also  over  the  olecranon,  the  malleoli,  the  knuckles,  and 
other  prominent  parts. 

Function  of  synovial  membranes.  —  As  previously  stated,  the 
function  of  synovial  membranes  is  similar  to  that  of  serous  mem- 
branes, but  synovial  membranes  are  associated  with  the  bones  and 
muscles. 

MUCOUS   MEMBRANES 

The  mucous  membranes,  unlike  the  serous  membranes,  line 
passages  and  cavities  which  communicate  with  the  exterior. 
Their  surfaces  are  coated  over  and  protected  by  mucus,  from 
which  the  membrane  derives  its  name.  The  mucous  membranes  of 
different  parts  are  continuous,  and  they  may  nearly  all  be  reduced 
to  two  great  divisions ;  namely,  (1)  gastropulmonary,  and  (2)  the 
genito-urinary. 

(1)  Gastropulmonary.  —  The  gastropulmonary  mucous  mem- 
brane covers  the  inside  of  the  alimentary  canal,  the  air-passages, 
and  the  cavities  communicating  with  them.  It  commences  at 
the  edges  of  the  lips  and  nostrils,  proceeds  through  mouth  and 
nose  to  the  throat,  and  thence  is  continued  throughout  the  entire 
length  of  the  alimentary  canal  to  the  anus.  At  its  origin  and 
termination  it  is  continuous  with  the  external  skin.  It  also 
extends  throughout  the  trachea,  bronchial  tubes,  and  air-sacs. 
From  the  interior  of  the  nose  the  membrane  is  prolonged 
into  the  frontal,  ethmoidal,  sphenoidal,  and  maxillary  sinuses, 
also  into  the  lacrimal  passages,  and  under  the  name  of  conjunc- 
tival  membrane,  over  the  fore  part  of  the  eyeball  and  inside  of 
the  eyelids,  on  the  edges  of  which  it  again  meets  with  the  skin. 
From  the  upper  and  back  part  of  the  pharynx  a  prolongation  ex- 


144 


ANATOMY  AND  PHYSIOLOGY     [CHAP.  VIII 


FRONTAL 
SINUSES 
DUCTS  OF 

LACHRYMAL  GLANDS 
UPPER  LIDS 
EYES' 

L.OWER  LID8~^> 
TEAR  DUCTsX 


UPPER  UP 


OIOAL  SINUSES 


AXILLARY 
NUSES 

DDLE  EARS 
MASTOIO 
CAVITIES 
EUSTACHIAW  TUBES 


COLON 


FIG.  97.  —  DIA- 
GRAM OF  THE  GASTRO- 
PULMONARY  MUCOUS 
MEMBRANE,  SHOW- 
ING THE  CONTINUITY 
OF  ALL  ITS  PARTS. 
(Gerrish.) 


tends  on  each  side,  along 
the  passage  to  the  ear, — 
Eustachian  tube,1  —  and 
offsets  in  the  alimentary 
canal  go  to  line  the  sal- 
ivary, pancreatic,  and  bili- 
ary ducts,  and  the  gall- 
bladder. 

(2)  Genito-urinary.  - 
The  genito-urinary  mu- 
cous membrane  lines  the 
inside  of  the  bladder,  and 
the  whole  urinary  tract 
from  the  interior  of  the 
kidneys  to  the  meatus 
urinarius,  or  orifice  of  the 
urethra;  in  the  female 
it  also  lines  the  vagina, 
uterus,  and  Fallopian 
(uterine)  tubes.  A  study 
of.  Figs.  98  and  99  will 
make  this  plain. 

Structure.  —  A  mucous 
membrane  is  composed  of 
four  layers  of  tissue  which 
occur  in  the  following 
order :  — 

(1)  Epithelium. 

(2)  Basement  membrane. 

(3)  Corium. 

(4)  Muscularis  mucosse. 

(1)  The  epithelium  is  the 
most  constant  part  of  a 
mucous  membrane,  being 
continued  over  certain  re- 
gions to  which  the  other 
parts  of  the  membrane 

1  Named  after  Eustachius,  a 
famous  anatomist. 


CHAP.  VIII]     SPECIAL   MEMBRANES   AND   GLANDS   145 

cannot  be  traced.  It  may  be.  scaly  and  stratified,  as  in  the 
throat;  columnar,  as  in  the  intestine;  or  ciliated,  as  in  the 
respiratory  tract. 

(2)  The  basement  membrane  consists  of  a  layer  of  flattened 
cells,  and  is  really  part  of  the  corium. 

(3)  The  corium  of  a  mucous  membrane  is  composed  of  either 
areolar   or   lymphoid   connective   tissue.     It   is   generally   much 
thicker  than  in  serous  or  synovial  membranes,  and  varies  much 
in  structure  in  different  parts. 


FIG.  98.  —  DIAGRAM  OF  THE  FEMALE  GENITO-URINARY  Mucous  MEMBRANE, 
SHOWING  CONTINUITY  OF  ALL  ITS  PARTS.     (Gerrish.) 

(4)  The  muscularis  mucosce  consists  of  a  thin  layer  of  muscular 
tissue. 

The  mucous  membranes  are  attached  to  the  parts  beneath  them 
by  areolar  tissue,  here  named  submucous.  This  differs  greatly 
in  quantity  as  well  as  in  consistency  in  different  parts.  The  con- 
nection is  in  some  cases  close  and  firm,  as  in  the  cavity  of  the  nose. 
In  other  instances,  especially  in  cavities  subject  to  frequent  vari- 
ations in  capacity,  like  the  oesophagus  and  the  stomach,  it  is  lax; 
and  when  the  cavity  is  narrowed  by  contraction  of  its  outer  coats, 
the  mucous  membrane  is  thrown  into  folds,  or  rugce,  which  dis- 
appear again  when  the  cavity  is  distended.  In  certain  parts  the 
mucous  membrane  forms  permanent  folds  that  cannot  be  effaced, 
and  these  project  conspicuously  into  the  cavity  which  it  lines. 
The  best-marked  example  of  these  folds  is  seen  in  the  small  in- 
testine, where  they  are  called  vahulce  conniwntes  l  (circular  folds), 

i  See  page  285, 


146 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  VIII 


which  are  doubtless  provided  for  increasing  the  amount  of 
absorbing  surface  for  the  products  of  digestion.  In  some  lo- 
cations the  free  surface  of  mucous  membrane  contains  minute 
glands,  or  is  covered  with  papillae,  villi,  or  cilia. 

Papillae.  —  The  papillae  are  best  seen  on  the  tongue ;  they  are 
small  processes  of  the  corium,  mostly  of  a  conical  shape,  containing 
blood-vessels  and  nerves,  and  covered  with  epithelium. 

Villi.  —  The  villi  are  most  fully  developed  on  the  mucous  coat 
of  the  small  intestine.  They  are  little  projections  of  the  mucous 
membrane,  covered  with  epithelium,  containing  blood-vessels  and 

lacteals,   and   are  favor- 
*ljp«***   ably    arranged    for    ab- 
'  sorbing  nutritive  matters 

from  the  intestines. 

Cilia.  —  For  descrip- 
tion of  cilia  see  page  29. 
Function  of  mucous 
membranes.  —  The  func- 
tion of  mucous  mem- 
branes is  (1)  protection, 

(2)  support    of    blood- 
vessels and   lymphatics, 

(3)  to    furnish    a    large 
amount    of    surface    for 
absorption. 

FIG.  99. -DIAGRAM   OF   THE    MALE   GENITO-         (l).    Tt       Protects       V 

URINARY  Mucous  MEMBRANE  SHOWING  CoNTi-   forming  a  lining  or  inside 

NUITY  OF  ALL  ITS  PARTS.     (Gerrish.)  i  '      £          n    ,-, 

skin  for  all  the  passages 

that  communicate  with  the  exterior.  These  passages  are  sub- 
ject to  the  contact  of  foreign  substances,  which  are  introduced 
into  the  body;  and  waste  materials,  which  are  expelled  from 
the  body.  The  mucus  which  it  secretes  is  a  thicker  and  more 
sticky  fluid  than  either  serum  or  synovia,  and  by  coating  the 
surface  lessens  the  possibility  of  irritation  from  food,  waste  ma- 
terials, or  secreted  substances.  The  cilia  of  the  respiratory  tract 
also  assist  in  the  function  of  protection.  They  keep  up  an  inces- 
sant motion,  and  thus  carry  mucus  toward  the  outlet  of  these 
passages.  Dust  and  foreign  materials  usually  become  entangled 
in  the  mucus  and  are  forced  out  with  it. 


CHAP.  VIII]     SPECIAL  MEMBRANES  AND   GLANDS   147 

(2)  The  redness  of  mucous  membranes  is  due  to  their  abun- 
dant supply  of  blood.    The  small  blood-vessels  which  convey  blood 
to  the   mucous  mem- 
branes  divide    in   the 

submucous  tissue,  and 
send  smaller  branches 
into  the  corium,  where 
they  form  a  network 
of  capillaries  just  under 
the  basement  mem- 
brane. The  lymphatics 
also  form  networks  in 
the  corium,  and  com- 
municate with  larger 
vessels  in  the  sub- 
mucous  tissue  below. 

(3)  The      modifica- 
tions of  mucous  mem- 
brane,    such     as    the 


CAPILLARY- 


COLUMNAR 
EPITHELIUM 


CAPILLARY 


NETWORK          LACTEAL  VESSEL 

FIG.  100.  —  AN  INTESTINAL  VILLUS. 
nified.) 


NETWORK 

(Highly  mag- 

nifiprM 

valvulse    conniventes,1 

and  villi,  are  largely  for  the  purpose  of  increasing  the  surface  for 

absorption,  and  also  to  enable  it  to  carry  more  blood-vessels  and 

lymphatics. 

CUTANEOUS  MEMBRANE 

By  this  term  is  indicated  the  membrane  which  covers  the  body 
and  ,is  commonly  spoken  of  as  skin.  It  is  a  complex  structure, 
and  has  several  functions  in  addition  to  serving  as  a  protective 
covering  for  the  deeper  tissues  lying  beneath  it.  It  will  be  more 
fully  considered  in  Chapter  XVIII. 

GLANDS 

A  gland  is  a  secreting  organ,  or  an  organ  which  abstracts  cer- 
tain materials  from  the  blood  and  makes  of  them  a  new  substance. 

The  simplest  form  of  a  gland  may  consist  of  just  one  cell,  such 
as  the  goblet  cells,2  or  may  be  a  mere  depression  on  the  surface  of 
a  membrane,  or  may  consist  of  a  vast  number  of  secreting  recesses. 
The  liver  and  pancreas  are  examples  of  the  latter.  No  matter 


See  Fig.  168. 


2  See  page  274. 


148 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  VIII 


what  the  size  or  shape  may  be,  all  glands  have  three  essential 
characteristics :  (1)  epithelial  cells  which  are  the  active  secreting 
agents,  (2)  a  liberal  blood  supply  from  which  the  material  for  the 
secretion  is  drawn,  (3)  they  are  under  the  direct  control  of  the  ner- 
vous system  and  secretion  is  their  response  to  stimulation,  just  as 
contraction  is  the  response  of  a  muscle.  The  usual  arrangement  is 


A        D         c       D 


FIG.  101.  —  DIAGRAM  SHOWING  DEVELOPMENT  OF  GLANDS:  A,  a  mere  dimple 
in  the  surface  or  a  simple  tubular  gland  ;  B,  enlargement  by  division  or  a  branched 
tubular  gland  ;  C,  enlargement  by  dilatation  or  a  saccular  gland  ;  D,  a  combination 
of  B  and  C  or  a  branched  saccular  gland ;  E,  a  compound  saccular  or  a  racemose 
gland ;  F,  development  of  method  of  E ;  G,  a  single  tube  intricately  coiled  or  a 
convoluted  tubular  gland. 

for  the  cells  to  cover  the  free  surface  of  a  basement  membrane, 
a  dense  network  of  capillaries  to  be  spread  upon  its  under  surface, 
and  nerve  fibrils  to  form  a  network  in  contact  with  the  cells. 
In  order  to  economize  space  and  to  provide  a  more  extensive 
secreting  surface,  the  membrane  is  generally  increased  by  dipping 
down  and  forming  variously  shaped  recesses.  (See  Fig.  101.) 
Classification.  —  The  secreting  glands  are  of  three  kinds  :  — 

1.  Simple. 

2.  Compound. 

3.  Ductless. 

1.  Simple  glands.  —  The  simple  glands  are  generally  tubular  or 
saccular  cavities,  which  open  upon  the  surface  by  a  single  duct. 
Sometimes  the  tube  is  so  long  that  it  coils  upon  itself,  as  in  the 
sweat  glands  of  the  skin. 

2.  Compound  glands.  —  In  the  compound  glands  the  cavities 
are  subdivided  into  smaller  tubular  or  saccular  cavities,  opening 
by  small  ducts  into  the  main  duct,  which  pours  the  secretion 
upon  the  surface.     If  composed  of  many  tubes,  either  straight  or 
convoluted,  they  are  called  compound  tubular  glands ;    if  com- 
posed of  groups  of  small  sacs,  they  are  called  racemose  glands. 


CHAP.  VIII]     SPECIAL  MEMBRANES  AND  GLANDS   149 

3.  Ductless  glands.  —  This  term  is  applied  to  a  collection  of 
glandular  structures  that  possess  no  ducts.  Whatever  secretion 
or  excretion  they  produce  is  discharged  into  the  blood,  either 
directly  or  indirectly  by  way  of  the  lymphatics. 

SECRETION 

A  new  substance,  the  product  of  a  gland,  elaborated  from 
the  blood  by  cell  action,  and  intended  for  use  in  the  body,  is  called 
a  secretion. 

For  purposes  of  study  we  may  divide  the  secretions  into  two 

groups :  — 

(1)  External  secretions. 

(2)  Internal  secretions. 

External  secretions.  —  This  term  is  used  to  designate  those 
secretions  of  glandular  tissues  which  are  carried  to  their  destina- 
tion by  a  duct.  All  of  the  digestive  fluids  —  saliva,  gastric  fluid, 
pancreatic  fluid,  bile,  and  intestinal  fluid  —  are  examples  of  ex- 
ternal secretions,  because  they  are  carried  off  from  the  respective 
glands  in  which  they  are  formed  by  means  of  ducts. 

Function.  —  The  function  of  the  external  secretions  is  dealt  with 
in  connection  with  the  organs  which  produce  them. 

Internal  secretions.  —  This  term  is  used  to  designate  those 
secretions  of  glandular  tissues  which  are  not  carried  off  to  the 
exterior  by  a  duct,  but  instead  are  discharged  into  the  blood  or 
lymph.  The  conception  is  that  probably  all  the  ductless  glands 
form  secretions  which  are  called  internal  secretions.  It  has  also 
been  shown  that  not  only  the  ductless  glands,  but  some  at  least  of 
the  typical  glands  provided  with  ducts,  may  give  rise  to  internal 
secretions.  For  example,  the  pancreas  forms  the  pancreatic  fluid 
and  discharges  it  by  means  of  a  duct  into  the  small  intestine.  In 
addition,  it  is  believed  that  the  pancreas  forms  an  internal  se- 
cretion which  passes  into  the  blood. 

Function.  —  The  quick  adaptive  reactions  by  which  emergencies 
are  met  and  by  which  the  various  bodily  activities  are  coordinated, 
are  functions  of  the  nervous  system,  but  the  internal  secretions 
have  a  great  deal  to  do  with  internal  adjustments.  They  contain 
chemical  substances  called  hormones,  which  are  carried  from  place 
to  place  by  the  blood.  A  hormone  is  a  substance  produced  in  a 


150 


ANATOMY  AND  PHYSIOLOGY     [CHAP.  VIII 


definite  locality  but  having  its  effect  elsewhere,  perhaps  at  a  great 
distance.1 

Excretion.  —  An  excretion  is  a  secretion,  except  that  the  excre- 
tion is  generally  formed  to  be  thrown  out  of  the  body,  whereas 
the  secretion  is  intended  for  use  in  the  body.  It  therefore 
follows  that  all  excretions  are  first  secretions,  and  some  substances 
are  made  use  of  before  they  are  eliminated.  For  instance,  bile 
serves  several  purposes  before  it  is  eliminated,  so  that  it  is  first 
a  secretion  and  then  an  excretion.  Urine,  on  the  other  hand,  is 
a  secretion,  but  is  formed  only  to  be  eliminated. 


SUMMARY 

f  Any  thin  expansion  of  tissue. 
Definition       {       '         ,     . 

[  An  enveloping  or  lining  tissue. 

1.  Serous  membranes. 

2.  Sy  no  vial  membranes. 

3.  Mucous  membranes. 

4.  Cutaneous  membranes. 


Varieties 


f  1.  Endothelium  —  a  single  layer  of  flat  cells. 
12. 


Serous  membranes  proper 


Corium  —  a  thin  layer  of  fibrous  tissue. 
Found  —  lining  closed  cavities  or  passages  that  do  not  communicate 
with  the  exterior.     They  are  moistened  by  serum. 

Pleurae  —  cover  the  lungs 
and  line  the  chest. 

Pericardium  •  covers 
the  heart  and  lines  the 
outer  fibrous  pericar- 
dium. 

Peritoneum  —  covers  the 
abdominal  and  the 
top  of  some  of  the  pel- 
vic organs,  lines  the 
abdominal  cavity. 

Heart: 

Blood-vessels. 

Lymphatics. 

Back  of  eye  —  capsule 
of  Tenon. 

Lining  membrane  of  the 
cavity  of  the  central 
nervous  system. 


Three  Classes 


Lining  membrane  of  the 
vascular  system 


Lining  membrane  of  cer- 
tain cavities 


1  See  Secretin,  page  322. 


CHAP.  VIII] 


SUMMARY 


151 


en  fe 
D  <; 

o2 

cd  PQ 
2  § 
W  y 


Function  —  Protection < 


1.  Furnishes  a  cover  or  lining 


Viscera. 
Vascular 

system. 
Certain 

cavities. 

2.  Furnishes  a  secretion  —  serum  —  which 
acts  as  a  lubricant. 


Consist  of 


Three  Classes 


Function  —  Protection 


f  1.  Imperfect  layer  of  irregularly  shaped  cells. 
2.  Layer  of  fibrous  tissue. 

f  Surround  cavities  of 
Articular  sy  no  vial  membranes  {  ..    .  . 

[     movable  joints. 

f  Form     sheaths     for 
Vaginal  synovial  membranes  , 

Sacs  interposed  be- 
tween   two     sur- 
faces which  move 
upon  each  other. 
Joints. 
Tendons. 
Sacs      between 
muscles    and 
bones. 

Furnishes    a    secretion  —  synovia  —  which 
acts  as  a  lubricant. 


Bursal  synovial  membranes 


Furnishes  a  cover  or  lining 


Gastropulmonary 


Found  —  Lining  passages  that  communicate  with  the  exterior  and  are 
protected  by  mucus. 

Alimentary  canal. 
Air-passages. 

Cavities    communicating    with 
Two  Divisions  both    alimentary    canal    and 

air-passages. 
f  Urinary  tract. 
1  Generative  organs. 
Stratified. 
Columnar. 
Ciliated. 

2.  Basement  membrane,  a  layer  of  flat  cells. 
Areolar  tissue,  or 
Lymphoid  tissue. 

4.  Muscularis    mucosse  —  thin   layer    of    muscular 
tissue. 


Genito-urinary 


Consist  of 


1.  Epithelium 


3.  Corium 


152 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  VIII 


Modifications 


Function 


/  (Esophagus. 
Rug*  -  temporary  folds  (  Stomach 

Valvulae  conniventes  —  permanent  folds  of  mucous 
membrane  found  in  small 
intestine. 

Papillae  —  conical  processes  of  mucous  membrane 
best   seen   on   tongue.     Contain   blood- 
vessels and  nerves. 
Villi  —  tiny  thread-like  projections  of  the  mucous 

membrane  of  small  intestine. 
Cilia  —  hair-like  processes. 

Inside  skin. 
Protection    Secretion  of  mucus. 

Action  of  cilia. 

Support  —  for  network  of  blood-vessels. 
Absorption  —  Various    modifications    increase  the 
surface. 


Definition  —  Glands  are  organs  that  form  secretions. 

A  single  cell,  or  many  cells  arranged  in  various  ways. 
Epithelial  cells. 


Structure 


Classification 


Essentials    A  liberal  blood-supply. 

Intimate  connection  with  nervous  system. 

1.  Simple  —  one  duct. 

2.  Compound  —  many  ducts. 

3.  Ductless  —  no  duct. 


Definition  —  Secretions  are  substances  elaborated  from  the  blood  by 
the  glands.     They  are  intended  to  perform  some  office  in  the  body. 
External  secretions  —  are  substances  formed  by  the 
simple  and  compound  glands  and  discharged  by 
means  of  a  duct. 

Internal  secretions  —  are  substances  formed  by  any 
kind  of  gland  and  discharged  into  the  blood  or 
lymph. 
External  secretions  —  studied  later. 

Essential  to  many  internal  ad- 


Classification 


Internal  secretions 


Function 

justments. 

Stimulate  by  means  of  hormones. 
Excretion  —  A  secretion  which  is  eliminated. 


CHAP.  VIII] 


SUMMARY 


153 


TABLE  OF  SECRETIONS  AND  EXCRETIONS 


SECRETION 

SECRETING  ORGANS 

REACTION 

MAIN  PURPOSE 

Mucus 

Mucous    cells    of 

Alkaline 

Lubricant  and  diluent. 

mucous  mem- 

brane 

Serum 

Serous          mem- 

Alkaline 

Lubricant  and  diluent. 

branes 

Tears 

Lacrimal  glands 

Alkaline 

To  moisten  the  conjunctiva. 

Saliva 

Salivary  glands 

Alkaline 

To  moisten  food  and  begin  the 

digestion  of  carbohydrates. 

Gastric 

Stomach 

Acid 

To  begin  the  digestion  of  pro- 

fluid 

teins. 

Pancreatic 

Pancreas 

Alkaline 

To  digest  proteins,  fats,   and 

fluid 

carbohydrates. 

Succus 

Intestines 

Alkaline 

To  stimulate  the  secretion  of 

entericus 

pancreatic  fluid,  also  digest 

proteins,    fats,    and    carbo- 

hydrates. 

Bile 

Liver 

Alkaline 

Part  of  the  bile  is  used  in  diges- 

tion and  reabsorbed.     Part 

is  a  true  excretion  (bile  pig- 

ments) . 

Milk 

Mammary  glands 

Alkaline 

Food. 

Sebum 

Sebaceous  glands 

Alkaline 

To  lubricate  the  skin. 

of  the  skin 

Sweat 

Sweat-glands     of 

Alkaline 

Helps  to  regulate   body  tem- 

skin 

perature.     Eliminates   water 

and  carbon  dioxide. 

Vaginal 

Vagina 

Acid 

Lubricant,  moistens  and  pro- 

tects. 

Urine 

Kidneys 

Acid 

Eliminates  water  and  urea. 

CHAPTER  IX 

VASCULAR  SYSTEM:     THE  BLOOD;     THE  CLOTTING  OF  BLOOD; 

LYMPH 

IT  is  helpful  to  recall  that  the  body  consists  of  an  enormous 
number  of  individual  cells,  and  that  each  cell  must  be  supplied 
with  materials  to  enable  it  to  carry  on  its  activities,  and  at  the 
same  time  it  must  have  the  waste  materials  that  are  the  result  of 
its  activities  removed.  Many  cells  are  far  from  the  source  of 
supplies  and  the  organs  of  elimination;  hence  the  need  of  a 
medium  to  distribute  supplies  and  collect  waste,  and  the  need  of  a 
system  so  that  the  distribution  will  be  orderly  and  systematic. 
These  two  needs  are  met  by  the  vascular  system,  the  divisions  of 
which  may  be  outlined  as  follows  :  — 


Vascular  System 


„      .  ..        '        f  Blood. 
Circulating  fluids    Lymph 


[  Blood  vascular. 


S^stems  1  Lymph  vascular. 


THE  BLOOD 

Characteristics.  —  The  most  striking  external  feature  of  the 
blood  is  its  well-known  color,  which  is  blood  red,  approaching  to 
scarlet  in  the  arteries,  but  of  a  dark  red  or  crimson  tint  in  the  veins. 

It  is  a  somewhat  sticky  liquid,  a  little  heavier  than  water; 
its  specific  gravity  is  about  1.055.  It  has  a  peculiar  odor,  a  saltish 
taste,  a  slightly  alkaline  reaction  when  tested  with  litmus,  and  a 
temperature  of  about  100°  F.  (37.8°  C.). 

Quantity  of  blood.  —  The  quantity  of  blood  contained  in  the 
body  of  an  adult  is  estimated  to  be  about  -fa  of  the  body  weight. 
This  proportion  was  formerly  said  to  be  about  -fs,  but  later  ex- 
periments seem  to  place  the  figure  at  -fa.  This,  in  an  individual 
weighing  160  pounds  (80  kilos),  would  weigh  about  8  pounds 
(4  kilos),  or  measure  4  quarts  (4  litres). 

154 


CHAP.  IX]  THE  BLOOD  155 

Functions  of  the  blood.  —  Blood  is  commonly  spoken  of  as 
the  nutritive  fluid  of  the  body.  This  is  correct,  but  it  is  more 
than  a  nutritive  fluid,  as  will  be  seen  from  the  following  list  of  its 
functions :  — 

(1)  It  serves  as  a  medium  for  the  interchange  of  gases,  e.g., 
carries  oxygen  to  the  cells  and  carbon  dioxide  from  the  cells. 

(2)  It  serves  as  a  medium  for  the  interchange  of  nutritive  and 
waste  materials.     It  carries  food  to  the  cells  and  waste  materials 
from  the  cells. 

(3)  It  serves  as  a  medium  for  the  transmission  of  internal  se- 
cretions.    The  presence  of  these  secretions  controls  the  chemical 
activities  of  cells. 

(4)  It  aids  in  equalizing  the  temperature  of  the  body.     Blood 
passing  through  a  tissue  which  is  undergoing  lively  metabolism  will 
have  a  higher  temperature  when  it  leaves  than  it  had  when  it 
entered.     This  extra  temperature  will  be  lost  in  passing  through  a 
tissue  that  is  not  so  active.     In  this  way  an  average  temperature 
is  maintained. 

(5)  It  aids  in  protecting  the  body  from  toxic  substances. 
Composition  of  the  blood.  —  Seen  with  the  naked  eye,  the  blood 

appears  opaque  and  homogeneous;  but  when  examined  with  a 
microscope  it  is  seen  to  consist  of  minute,  solid  particles  called 
cells  or  corpuscles,  floating  in  a  transparent,  slightly  yellowish 
fluid  called  plasma. 

Red  or  erythrocytes. 


Cells  or  Corpuscles 


White  or  leucocytes. 


d  Blood-plates. 

Plasma 

Red  cells.  —  The  red  cells  are  usually  described  as  being  cir- 
cular biconcave  discs,  with  rounded  edges.  The  average  size  is 
3  2*0 o  of  an  inch  (0.008  mm.)  in  diameter.  Because  of  their 
extremely  small  size,  the  red  cells  do  not  appear  red  when  viewed 
singly  with  a  microscope,  but  merely  of  a  yellowish  red  tinge,  or 
yellowish  green  in  venous  blood.  It  is  only  when  great  numbers 
of  them  are  gathered  together  that  a  distinctly  red  color  is  pro- 
duced. 

Authorities  differ  regarding  the  structure  of  the  red  cells.  Some 
describe  them  as  consisting  of  a  colorless,  filmy,  elastic  framework 
infiltrated  in  all  parts  by  a  red  coloring  matter  termed  haemoglobin. 


156  ANATOMY  AND   PHYSIOLOGY       [CHAP.  IX 

Others  describe  them  as  consisting  of  a  colorless  elastic  envelope 
enclosing  a  solution  of  haemoglobin.  In  either  case  it  is  correct 
to  consider  them  as  packets  of  haemoglobin  moving  passively  at 
the  mercy  of  the  blood  current.  They  have  no  nuclei,  are  soft, 
flexible,  and  elastic,  so  that  they  readily  squeeze  through  aper- 
tures and  passages  narrower  than  their  own  diameters,  and  im- 
mediately resume  their  proper  shape. 

Hcemoglobin.  —  Haemoglobin  is  a  substance  which  is  formed  of 
an  iron  salt  and  a  protein.  In  the  presence  of  oxygen  it  has  the 
power  to  combine  with  it  to  form  an  unstable  compound  called 
oxyhsemoglobin,  and  in  an  environment  where  oxygen  is  scarce, 
it  gives  up  this  oxygen,  and  is  then  known  as  reduced  haemoglobin. 

Hemolysis  or  "  Laking."  -  Under  certain  circumstances  haemo- 
globin may  pass  out  of  the  red  cells  into  the  surrounding  fluid. 
This  process  is  known  as  hemolysis  or  "  laking  "  and  a  few  of  the 
ways  in  which  it  may  be  brought  about  are  (1)  by  adding  water 
to  the  blood,  (2)  by  adding  to  it  the  blood  of  certain  other  ani- 
mals,1 and  (3)  by  adding  to  it  various  toxins  such  as  snake  venom 
or  certain  products  of  bacterial  activity. 

Number  of  red  cells.  —  The  average  number  of  red  cells  in  a 
cubic  millimetre  of  healthy  blood  is  given  as  5,000,000  for  men, 
and  4,500,000  for  women.  Pathological  conditions  may  cause  a 
marked  diminution  in  number,  and  differences  have  been  observed 
even  in  health.  The  number  varies  with  altitude ;  temperature ; 
the  constitution,  nutrition,  and  manner  of  life;  with  age,  being 
greatest  in  the  foetus  and  new-born  child ;  with  the  time  of  day, 
showing  a  diminution  after  meals ;  in  the  female  menstruation  is 
accompanied  by  an  increase  and  pregnancy  by  a  decrease.  The 
condition  known  as  anemia  may  be  due  to  a  diminished  number 
of  red  cells  wThich  means  a  diminished  supply  of  oxygen,  and  a 
consequent  interference  with  the  processes  of  metabolism. 

Function  of  the  red  cells.  —  The  red  cells,  or  erythrocytes, 
by  virtue  of  the  haemoglobin  which  they  contain,  are  emphati- 
cally oxygen  carriers.  Exposed  to  the  air  in  the  lungs  the  haemo- 
globin becomes  fully  charged  with  detachable  oxygen  and  is  known 
as  oxyhaemoglobin.  The  red  cells  carry  this  oxyhaemoglobin  to 

1  Before  transfusing  blood  from  one  human  being  to  another,  the  blood  of  the 
donor  is  always  tested  in  several  ways.  The  purpose  of  one  test  is  to  make  sure 
that  it  will  not  hemolyze  the  red  cells  of  the  recipient. 


CHAP.  IX]  THE  BLOOD  157 

the  tissues,  where  it  gives  up  the  loosely  engaged  oxygen.  It  is 
then  known  as  reduced  haemoglobin  and  is  ready  to  be  carried  to 
the  lungs  for  a  fresh  supply.  The  color  of  the  blood  is  dependent 
upon  the  combination  of  the  haemoglobin  with  oxygen ;  when  the 
haemoglobin  has  its  full  complement  of  oxygen,  the  blood  has  a 
bright  red  hue;  when  the  amount  is  decreased,  it  changes  to  a 
dark  crimson  hue.  The  scarlet  blood  is  usually  found  in  the  ar- 
teries, and  is  called  arterial ;  the  dark  crimson  in  the  veins,  and 
is  called  venous  blood. 

Life  cycle  of  the  red  cells.  —  The  red  cells  like  all  the  cells  of  the 
body  have  a  definite  tefm  of  existence.  There  is  every  reason  to 
believe  that  this  term  of  existence  is  very  short,  possibly  not  more 
than  a  few  days.  They  originate  in  the  red  marrow  of  the  bones. 
Before  entering  the  blood  stream  they  lose  their  nuclei,  and  this 
of  itself  suggests  that  they  do  not  live  a  great  while  in  the  circu- 
lation. It  has  been  suggested  that  their  destruction  takes  place 
in  the  liver,  spleen,  or  lymph  nodes.1 

White  cells.  —  The  white  cells  are  typical  cells  containing  a 
nucleus,  sometimes  even  two  or  three  nuclei.  They  are  variable  in 
size,  but  are  somewhat  larger  than  the  red  cells. 

Number  of  white  cells.  —  The  average  number  of  white  cells  in 
a  cubic  millimetre  of  healthy  blood  is  from  5000  to  7000.  A  marked 
increase  in  number  is  designated  as  leucocytosis ,  a  marked  decrease 
as  leucopenia.  Leucocytosis 2  occurs  under  normal  conditions, 
such  as  digestion,  exercise,  or  cold  baths.  It  also  occurs  under 
abnormal  conditions,  and  a  knowledge  of  the  variations  under 
pathological  conditions  is  an  important  aid  in  diagnosis. 

1  Some  authors  give  the  weight  of  man  as  70  K.,  and  as  1  K.  equals  2.28  Ib.  or 
1000  gm.,  this  reduced  to  grams  would  give  70,000  gm.  as  the   weight  of  man. 
We  are  taught  that  the  blood  in  the  body  equals  ^  of  the  body  weight.     ^V  of 
70,000  gm.  is  3500  gm.     In  every  100  gm.  of  blood  there  are  14  gm.  of  hematin 
so   that  3500   gm.   of    blood   would   contain   3500    divided    by    100,   multiplied 
by  14,  which  equals  490  gm.     This  means  that  the  body  contains   490  gm.   of 
hematin.     The  destruction  products  of  48  gm.  of  hematin  are  eliminated  by  the 
liver  daily.     Hence,  it  would  take  as  many  days  to  eliminate  490  gm.  as  48  gm. 
is  contained  in  it.     This  equals  ten  days  plus,  and  gives  us  the  approximate  life  of 
a  red  blood  cell.     According  to  some  authors,  the  daily  loss  of  pigment  is  much  less, 
hence  the  life  of  the  red  cells  would  be  much  longer. 

2  Leucocytosis  is  found  in  practically  all  infectious  processes  except  typhoid  and 
tuberculosis.     A  leucocytosis  is  demonstrated  by  a  "blood  count,"  i.e.,  counting  the 
white  blood  cells  in  a  given  volume  of  a  known  dilution  of  blood,  using  special 
pipettes  and  ruled  slides,  under  the  microscope.     Any  considerable  increase,  i.e., 
over  8000,  is  evidence  of  a  leucocytosis. 


158 


ANATOMY  AND  PHYSIOLOGY        [CHAP.  IX 


Varieties  of  white  cells.  —  At  least  five  varieties  have  been  studied 
and  described.     They  are  classified  under  two  main  groups  :  — 

(1)  Lymphocytes. 

(2)  Leucocytes. 

The  most  marked  difference  is  in  the"  nuclei  and  in  the  amount  of 
amoeboid  movement  exhibited. 


FIG.  102.  —  VARIETIES  OF  WHITE  CELLS  FOUND  IN  HUMAN  BLOOD.  When 
stained  with  blood  stains  various  kinds  of  white  cells  can  be  distinguished.  Five 
varieties  are  shown  above.  A,  lymphocyte;  B,  C,  mononuclear  leucocytes; 
D,  polynuclear  leucocyte ;  E,  eosinophile  leucocyte  ;  F,  mast  cell. 

Each  of  these  groups  may  be  subdivided  into  two  or  more  sub- 
groups, and  some  authorities  hold  that  each  variety  has  some 
special  function,  but  this  has  not  been  proven. 

Amoeboid  movements  of  white  cells.  —  One  distinctive  property 
of  white  cells  is  their  power  of  making  amoeboid  movements, 
which  enables  them  to  change  their  form  and  escape  through  the 
walls  of  the  blood  capillaries  into  the  surrounding  tissues.  This 
property  has  earned  for  them  the  title  of  wandering  cells  and  the 
process  is  spoken  of  as  migration.  It  occurs  under  normal  con- 
ditions, but  is  vastly  accelerated  under  pathological  conditions. 

Function  of  the  white  cells.  —  Many  functions  are  ascribed  to 
the  white  cells,  and  many  theories  are  advanced  in  support  of 


CHAP.  IX]  THE  BLOOD  159 

these  functions.  A  few  of  the  most  important  are  (1)  they  act 
as  protective  agents,  (2)  they  aid  in  the  absorption  of  digested 
fats  and  proteins  from  the  intestines,1  (3)  they  assist  in  clotting 
of  the  blood.2  Their  function  of  protection  is  very  important 
and  it  has  been  suggested  that  it  may  be  accomplished  in  two 
ways :  — 

(a)  By  contributing  to  the  formation  of  antibodies;3  (b)  by 
virtue  of  their  amoeboid  movement  they  can  project  irregular  pro- 
cesses which  are  very  sticky,  so  that  the  bacteria  stick  to  them, 
and  are  ingested  by  them.  This  process  is  called  phagocytosis 
and  has  earned  for  them  the  name  of  phagocytes.  According  to 
some  authorities  this  property  depends  upon  the  presence  in  the 
plasma  of  a  certain  class  of  antibodies  called  opsonins  4  which  in 
some  way  prepares  bacteria  for  ingest  ion  by  the  leucocytes. 

Inflammation.  —  When  any  of  the  tissues  become  inflamed 
either  as  the  result  of  injury  or  infection,  the  first  effect  is  irritation, 
followed  by  an  increased  supply  of  blood  to  the  part.  If  the  irri- 
tation continues  or  is  severe,  the  flow  of  blood  begins  to  slacken, 
and  a  condition  of  stasis  or  engorgement  results.  The  white 
cells  become  particularly  active  and  migrate  into  the  infected 
tissues  in  large  numbers.  Some  of  the  blood  plasma  exudes,  and 
a  small  number  of  red  cells  are  forced  through  the  capillary  walls.5 
This  general  condition  is  described  as  inflammation,  and  the 
symptoms  of  pain,  heat,  redness,  and  swelling  are  due,  (1)  to 
the  increased  supply  of  blood,  (2)  to  the  engorgement  of  the  blood- 
vessels, and  (3)  to  the  collection  of  fluid  in  the  tissues,  which  is 
spoken  of  as  inflammatory  exudate.  Under  these  conditions  a 
death  struggle  between  the  leucocytes  and  bacteria  takes  place. 
If  the  leucocytes  are  victorious,  they  not  only  kill  the  bacteria  but 
remove  every  vestige  of  the  struggle,  and  find  their  way  back  to 
the  blood.  If  the  bacteria  are  victorious,  and  suppuration  en- 
sues, the  leucocytes  become  pus  cells.  Also,  in  the  case  of  a 
wound,  the  leucocytes,  by  virtue  of  their  amoeboid  movements, 
escape  from  the  blood-vessels,  accumulate  in  the  region  of  the 
wound,  and  act  as  barriers  against  infection. 

1  See  page  325.  a  gee  page  163.  8  See  page  162. 

4  From  opso'no,  I  prepare  food  for. 

6  This  passive  ability  of  red  corpuscles  to  pass  through  the  capillary  walls  is 
called  diapedesis. 


160  ANATOMY  AND   PHYSIOLOGY        [CHAP.  IX 

Life  cycle  of  the  white  cells.  —  The  white  cells  like  all  other  cells 
have  a  definite  term  of  existence.  We  do  not  know  the  length 
of  this  term,  or  where  they  are  destroyed,  except  that  large  num- 
bers are  lost  in  the  battle  waged  against  bacteria,  others  by  hem- 
orrhage, and  others  may  be  converted  into  granulation  tissue. 
These  lost  leucocytes  are  replaced  by  new  leucocytes  which  re- 
sult from  the  division  of  former  leucocytes.  This  division  usually 
takes  place  in  the  lymph  nodes  and  the  spleen. 

Differences  between  white  and  red  cells.  - 

(1)  White  cells  are  larger  than  red  cells,  but  normally  are  present 
in  smaller  numbers. 

(2)  They  have  no  pigment  or  haemoglobin,  hence  are  colorless. 

(3)  On  account  of  the  property  of  amoeboid  movement  their 
shape  varies. 

(4)  They  always   have   a    nucleus,    sometimes  two   or  three 
nuclei. 

(5)  There  are  five  varieties  that  differ  in  microscopical  structure 
and  possibly  in  function. 

(6)  During  circulation  they  keep  close  to  and  even  seem  to 
adhere  to  the  walls  of  the  vessels,  while  the  red  cells  keep  in  the 
middle  of  the  stream. 

(7)  By  virtue  of  their  amoeboid  movement  they  escape  through 
the  walls  of  the  capillaries  and  are  found  in  the  tissue  spaces. 
They  are  also  found  in  lymph,  chyle,  and  pus. 

(8)  The  functions  of  the  white  cells  are  quite  different  from  the 
function  of  the  red  cells. 

Blood-plates.  —  They  are  disc-shaped  bodies,  which  vary  in 
size  but  are  always  smaller  than  the  red  cells.  Their  origin,  fate, 
and  function  are  still  open  questions.  It  is  not  decided  whether 
they  are  to  be  considered  as  independent  cells  or  as  fragments  of 
disintegrated  cells.  There  is  considerable  evidence  to  show  that 
they  take  part  in  the  process  of  clotting.  (See  page  163.) 

Plasma.  —  The  ulasma  of  the  blood  is  of  a  clear,  slightly  yel- 
lowish color.  It  is  a  very  complex  fluid  and  contains  a  great 
variety  of  substances  as  might  be  inferred  from  its  double  relation 
to  the  cells,  serving  as  a  source  of  nutrition  and  as  a  means  of  re- 
moving the  waste  products  that  result  from  their  functional  ac- 
tivity. It  consists  of  water  holding  in  solution  or  suspension :  — 


CHAP.  IX] 


THE  BLOOD 


161 


Extractives 


Represent  waste  products. 


f  Fibrinogen. 

Proteins |  Paraglobulin  or  serum-globulin. 

[  Serum-albumin. 
Sugars. 
Fats. 
Urea 
Uric  acid 
Hippuric  acid 
Creatin 
Creatinin 
f  Chlorides 
I  Sulphates 
I  Phosphates 
[  Carbonates 
f  Oxygen. 
Gases     .     .     .     .     .     .  I  Nitrogen. 

[  Carbon  dioxide. 
Internal  Secretions 
Enzymes 


Inorganic  Salts 


of 


f  Sodium. 
|  Calcium. 
[  Magnesium. 


Special  Substances 


Antithrombin. 

Prothrombin. 

Epinephrin. 

Antigens  and  Antibodies. 


Proteins  of  the  blood-plasma.  —  Three  proteins  are  usually 
described  as  existing  in  the  plasma  of  circulating  blood,  i.e.,  fibrino- 
gen,  paraglobulin,  and  serum-albumin.  The  first  two  of  these 
proteins  belong  to  the  group  of  globulins  and  hence  have  many 
properties  in  common.  Serum-albumin  belongs  to  the  group  of 
albumins  2  of  which  white  of  egg  constitutes  another  member. 

Many  experiments  seem  to  indicate  that  fibrinogen  may  be 
formed  in  the  liver.  When  blood  is  shed  fibrinogen  is  changed 
to  an  insoluble  protein  known  as  fibrin.3  The  significance  of 
paraglobulin  and  serum-albumin  is  obscure.  Not  long  ago 
they  were  thought  to  be  formed  continually  in  the  cells  lining 
the  intestine,  and  consumed  as  food  by  the  tissues,  but  this 
does  not  seem  so  probable  since  the  presence  of  amino-acids4 
in  the  blood  has  been  shown.  They  are  now  looked  upon  as 

1  This  list  is  by  no  means  complete.     For  more  detailed  analysis  the  student  is 
referred  to  the  standard  books  on  Physiology  and  Physiological  Chemistry. 

2  Albumins  and  globulins  give  the  same  general  tests ;   they  are  both  coagulated 
by  heat,  and  the  chief  difference  is  in  their  solubilities. 

'  See  page  163.  <  See  page  308. 

M 


162  ANATOMY  AND   PHYSIOLOGY        [CHAP.  IX 

a  rather  stable  and  permanent  mass,  little  subject  to  depletion 
and  hence  requiring  little  renewal. 

Extractives.  —  Extractives  are  substances  other  than  proteins 
that  may  be  extracted  from  dried  blood  by  special  methods. 

Sugar  in  the  form  of  glucose  is  present  under  normal  conditions 
in  the  amount  of  0.1  to  0.15  per  cent.  A  temporary  increase 
in  the  amount  of  sugar  may  follow  the  ingestion  of  a  large 
quantity. 

Fat  is  found  in  the  plasma  in  about  the  same  proportion  as  sugar. 
It  is  much  more  subject  to  variation,  rising  notably  after  a  meal 
in  which  there  was  much  fat. 

Waste  products  found  in  the  plasma  represent  the  end  products 
resulting  from  the  oxidation  of  our  food.  Due  to  the  efficiency  of 
the  kidneys,  they  occur  in  very  small  quantities. 

Salts.  —  The  salts  found  in  the  blood  are  derived  from  the 
food  and  from  the  chemical  reactions  going  on  in  the  body.  The 
most  abundant  is  sodium  chloride. 

Gases.  —  Oxygen,  nitrogen,  and  carbon  dioxide  gas  are  found 
in  the  blood.  Carbon  dioxide  is  the  result  of  oxidation  in  the 
tissues,  and  is  found  in  both  arterial  and  venous  blood,  but  the 
quantity  is  greater  in  venous  blood. 

Internal  secretions.  —  The  blood  serves  as  a  medium  to  carry 
internal  secretions.  (See  page  149.) 

Enzymes.  —  See  page  311. 

Special  substances.  —  Antithrombin  and  prothrombin  are  con- 
sidered in  connection  with  the  clotting  of  blood. 

Epinephrin.  —  It  is  generally  believed  that  the  blood  receives 
a  constant  supply  of  epinephrin  from  the  adrenal  glands.  (See 
page  345.) 

Antigens  and  Antibodies.  —  The  term  antigen  is  applied  to 
substances  which  stimulate  the  formation  of  antibodies.  The 
term  antibodies  includes  all  defensive  substances  found  in  the 
blood,  e.g.,  agglutinins,  opsonins,  'antitoxins,  immune  bodies,  etc. 
When  the  body  is  invaded  by  pathogenic  bacteria,  the  toxic  sub- 
stances produced  by  these  organisms  (antigens)  stimulate  the 
tissues  to  form  specific  antitoxins  (antibodies)  which  are  capable 
of  neutralizing  the  action  of  the  bacterial  toxins. 


CHAP.  IX] 


THE  BLOOD 


163 


FIG.  103.  —  BOWL  OF 
RECENTLY  CLOTTED 
BLOOD,  SHOWING  THE 
WHOLE  MASS  UNI- 
FORMLY SOLIDIFIED. 
(Dalton.) 


THE   CLOTTING  OF  BLOOD 

Blood  when  drawn  from  the  blood-vessels  of  a  living  body  is 
perfectly  fluid.  In  a  short  time  it  becomes  viscid,  and  this  vis- 
cidity increases  rapidly  until  the  whole  mass 
of  blood  becomes  a  complete  jelly.  If  the 
blood  in  this  jelly  stage  be  left  untouched 
in  a  glass  vessel,  a  few  drops  of  an  almost 
colorless  fluid  soon  make  their  appearance 
on  the  surface  of  the  jelly.  Increasing  in 
number  and  running  together,  the  drops  after 
a  while  form  a  superficial  layer  of  pale  straw- 
colored  fluid.  Later  on,  similar  layers  of 
the  same  fluid  are  seen  at  the  sides,  and 
finally  at  the  bottom  of  the  jelly,  which, 
shrunk  to  a  smaller  size  and  of  firmer  con- 
sistency, now  form  a  clot,  floating  in  a  fluid  which  is  called  serum. 
If  a  portion  of  the  clot  is  examined  under  the  microscope,  it  is 
seen  to  consist  of  a  network  of  fine  fibrils,  in  the  meshes  of  which 
are  entangled  the  red  and  some  of  the  white 
cells  of  the  blood.  The  fibrils  are  composed 
of  fibrin,  which  is  essential  to  the  formation 
of  a  clot.  The  formation  of  insoluble  fibrin 
from  soluble  fibrinogen  is  an  instance  of 
enzyme  action  and  is  comparable  to  the 
clotting  of  milk  under  the  influence  of  ren- 
nin.  The  enzyme  which  causes  the  fibrin 
to  form  is  called  thrombin,  and  exists  in 
the  blood  in  an  inactive  form  called  pro- 
thrombin.  Prothrombin  may  be  converted 
to  active  thrombin  by  the  action  of  calcium, 
but  in  circulating  blood  this  is  prevented 
by  another  enzyme  called  antithrombin.  This  antithrombin 
must  be  neutralized  to  permit  the  calcium  to  react  with  pro- 
thrombin  to  form  thrombin,  which  in  turn  reacts  with  the  fibrino- 
gen to  form  fibrin.  One  theory  is  that  this  neutralizing  or 
thromboplastic  1  substance  is  furnished  by  the  blood-plates,  leu- 


FIG.  104.  —  BOWL  OF 
CLOTTED  BLOOD  AFTER 
TWELVE  HOURS,  SHOW- 
ING THE  CLOT  CON- 
TRACTED AND  FLOATING 
IN  THE  FLUID  SERUM. 
(Dalton.) 


1  Various  preparations  of  thromboplastic  material  are  obtainable,  and  are  in 
use  to  check  hemorrhage.     Some  are  applied  externally  to  a  bleeding  surface  such 


164  ANATOMY  AND  PHYSIOLOGY        [CHAP.  IX 

cocytes,  and  cells  of  the  tissues  over  which  the  blood  flows  when 
it  escapes  from  the  blood-vessels. 
This  may  be  represented  in  diagrammatic  form  as  follows :  — 

Cellular  elements  of  blood  and  tissues— >thromboplastic  substance. 
Thromboplastic  substance  neutralizes  antithrombin. 
Prothrombin  +  calcium— >thrombin. 
Thrombin  +  fibrinogen  =  clot. 

Value  of  clotting.  —  This  property  is  of  very  great  importance 
in  the  arrest  of  hemorrhage.  The  clot  formed  closes  the  openings 
of  wounded  vessels,  and  the  procedures  used  to  check  hemorrhage 
are  directed  toward  hastening  the  formation  of  a  clot,  and  stimu- 
lating the  blood-vessels  to  contract  so  that  a  smaller-sized  clot 
will  be  sufficient. 

The  clotting  power  of  the  blood  differs  in  different  individuals 
and  in  rare  cases  is  so  slight  that  the  most  trivial  operation  involv- 
ing hemorrhage  is  attended  with  great  danger.  This  condition 
is  known  as  hemorrhagic  diathesis  or  hemophilia. 

Conditions  affecting  clotting.  —  Clotting  is  hastened  by :  - 

(1)  A  relatively  high  temperature,  e.g.,  the  use  of  hot  towels 
to  check  bleeding  from  the  stump  of  an  amputated  limb ;  the  use 
of  hot  douches  to  check  postpartum  hemorrhage. 

(2)  Contact  with  any  foreign  substance,  or  rough  surface  such 
as  gauze. 

(3)  Injury  to  the  walls  of  the  blood-vessels. 

(4)  Rest. 

If  blood  is  contained  in  a  dish  agitation  hastens  the  process 
of  clotting,  because  like  the  first  three  conditions  it  favors  the 
formation  of  thromboplastic  substance. 

Clotting  is  hindered  by :  — 

(1)  A  very  low  temperature.     Cold  hinders  the  formation  of  a 
clot  but  is  often  used  to  check  hemorrhage,  because  it  stimulates 
the  blood-vessels  to  contract. 

(2)  Contact  with  the  lining  of  the  heart  and  blood-vessels. 

(3)  The  addition  of  strong  acids  or  alkalies,  neutral  salts,  oil 
or  other  viscid  substances,  certain  organic  ferments,  or  a  large 
quantity  of  water. 

(4)  Absence  of  calcium  salts. 

as  is  left  after  an  operation  for  removal  of  tonsils ;   or  injected  into  the  tissues,  and 
one,  i.e.,  cephalin-protein,  is  introduced  directly  into  the  blood-vessels. 


CHAP.  IX]  THE  BLOOD  165 

(5)  Absence  of  fibrinogen. 

(6)  Removal  of  fibrin.     If  fresh  blood,  before  it  has  time  to 
clot,  be  whipped  with  a  bundle  of  twigs,  the  fibrin  will  form  on 
the  twigs,  and  if  the  whipping  of  the  blood  be  continued  until 
after  the  fibrin  has  been  deposited  on  the  twigs,  the  blood  left  in 
the  vessel  will  be  found  to  have  lost  the  power  of  clotting.     Such 
blood  is  called  defibrinated. 

Why  blood  does  not  clot  within  the  blood-vessels.  —  In  ac- 
cordance with  the  theory  of  clotting  which  we  have  considered, 
blood  does  not  clot  within  the  blood-vessels  because  of  the  presence 
of  antithrombin. 

Intravascular  clotting.  —  It  is  well  known  that  clots  occasionally 
form  within  the  blood-vessels.  The  most  frequent  causes 
are :  — 

(1)  When  the  internal  coat  of  a  blood-vessel  is  injured,  as  for 
instance  by  a  ligature,  the  endothelial  cells  are  altered  and  may 
act  as  a  foreign  substance.     If  in  addition  there  is  a  stasis  of 
blood  at  this  point,  disintegration  of  the  blood-plates  and  white 
cells  may  result  in  the  formation  of  thrombin  and  a  clot. 

(2)  Any  foreign  material,  even  air,  that  is  introduced  into  the 
blood  and  not  absorbed,  may  stimulate  the  formation  of  thrombin 
and  a  clot. 

Thrombus  and  embolus.  —  A  clot  which  forms  inside  a  blood- 
vessel is  called  a  thrombus.  A  thrombus  may  be  broken  up  and 
disappear,  but  the  danger  is  that  it' may  be  carried  to  some  point 
in  an  important  vessel  where  it  acts  as  a  wedge,  blocks  circulation, 
and  may  cause  instant  death.  A  thrombus  that  becomes  dis- 
lodged from  its  place  of  formation  is  called  an  embolus. 

Regeneration  of  the  blood  after  hemorrhage.  —  A  large  portion 
of  the  total  amount  of  blood  in  the  body  may  be  lost  suddenly  by 
hemorrhage  without  producing  a  fatal  result.  It  is  probable 
that  a  healthy  individual  may  recover  from  the  loss  of  as  much  as 
three  per  cent  of  the  body  weight,  provided  the  lost  blood  is  at 
once  replaced  by  a  solution  having  the  same  degree  of  concentra- 
tion (i.e.,  isotonic)  and  containing  one  or  more  of  the  important 
salts  of  the  blood.  Physiological  saline  solution,  i.e.,  sodium 
chloride  0.7  to  0.9  per  cent,  fulfills  these  conditions,  and  is  usually 
introduced  directly  into  a  vein.  This  operation  is  called  intra- 
venous infusion,  and  the  benefits  derived  from  it  are :  — 


166 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  IX 


(1)  The  heart-beat  is  increased,  because  it  must  make  stronger 
contractions  to  propel  the  extra  fluid. 

(2)  The  volume  of  the  circulating  fluid  is  sufficiently  increased 
to  maintain  normal  conditions  of  pressure  and  velocity. 

(3)  The  red  cells  are  kept  in  rapid  circulation  and  thus  loss  of 
oxygen  to  the  tissues  is  prevented. 

(4)  The  tissue  cells  are  provided  with  water  and  thus  protected 
from  the  bad  effects  that  would  follow  the  withdrawal  of  water. 

Plasma  is  regenerated  with  some  rapidity  (probably  within  a 
few  hours)  but  it  may  take  days  or  even  weeks  before  the  number 
of  red  cells  and  the  quantity  of -haemoglobin  is  replaced. 


LYMPH 

Lymph  is  a  colorless  liquid  found  in  the  lymph-vessels  and 
in  all  the  tissue-spaces  of  the  body.  It  is  slightly  alkaline,  has  a 
salty  taste,  and  no  odor.  When  examined  with  the  microscope, 
it  is  seen  to  consist  of  a  clear  liquid  with  white  cells  floating  in 
it.  In  composition  it  resembles  the  blood-plasma,  as  indicated 
in  the  following  table  :  - 


BLOOD 


LYMPH 


Specific  gravity  about  1.055 

Contains  red  cells 

Contains  white  cells 

Contains  blood-plates 

A  high  content  of  proteins 

A  low  content  of  waste  products 

Normally  —  clots  quickly  and  firmly 


Specific  gravity  about  1.015 
Does  not  contain  red  cells  (normally) 
Contains  white  cells 
Does  not  contain  blood-plates 
A  low  content  of  proteins 
A  higher  content  of  waste  products 
Clots  slowly  and  does  not  form  a 
firm  clot 


Sources  of  lymph.  —  By  the  action  of  physical  and  chemical  pro- 
cesses, the  details  of  which  are  not  entirely  understood,  the  plasma 
of  the  blood  makes  its  way  through  the  thin  walls  of  the  capil- 
laries into  such  spaces  as  exist  between  the  cells  forming  the 
tissues.  Some  physiologists  claim  that  the  combined  action  of  the 
physical  processes  of  filtration,  diffusion  and  osmosis,  is  sufficient 
to  account  for  the  formation  of  lymph.  Others  claim  that  in  ad- 
dition it  is  necessary  to  assume  an  active  secretory  process  on  the 


CHAP.  IX]  THE  LYMPH  167 

part  of  the  endothelial  cells  composing  the  capillary  walls.  This 
plasma  plus  the  leucocytes  that  have  left  the  vessels  by  migration 
make  up  the  lymph.  Besides  this  the  lymph  that  fills  the  lacteals 
of  the  intestinal  villi  absorbs  some  of  the  products  of  digestion, 
especially  the  fats. 

The  portion  of  the  lymph  that  has  absorbed  the  fats  is  milky 
in  appearance,  and  is  called  chyle.  The  lymph,  broadly  speak- 
ing, is  dilute  blood-plasma  minus  its  red  cells.  The  chyle  is  lymph 
plus  a  very  large  quantity  of  minutely  divided  fat. 

Functions  of  the  lymph.  —  The  lymph  bathes  all  portions  of 
the  body  not  reached  by  the  blood.  It  delivers  to  the  cells  the 
material  each  cell  needs  to  maintain  its  functional  activity,  and 
picks  up  and  returns  to  the  blood  the  products  of  this  activity, 
which  products  may  be  simple  waste,  or  matters  capable  of  being 
made  use  of  by  some  other  tissue.  There  is  thus  a  continual  in- 
terchange going  on  between  the  blood  and  the  lymph.  This 
interchange  is  effected  by  means  of  osmosis  and  dialysis. 

Osmosis  and  dialysis.  —  The  lymph  becomes  altered  by  the 
metabolic  changes  of  the  tissues  which  it  bathes,  and  we  have  two 
different  fluids,  separated  by  the  moist  membrane  which  forms  the 
walls  of  the  blood-vessels,  —  the  lymph  in  the  tissues  outside  the 
walls  of  the  capillaries  and  the  blood  inside  the  capillary  walls. 
Some  of  the  constituents  of  the  lymph  pass  into  the  blood,  while 
some  of  the  constituents  of  the  blood  pass  into  the  lymph,  by  the 
processes  of  osmosis  and  dialysis.1 

In  consequence  of  the  different  wants  and  wastes  of  different 
tissues  at  different  times,  both  the  lymph  and  blood  must  vary  in 
composition  in  different  parts  of  the  body.  But  the  loss  and  gain 
is  so  fairly  balanced  that  the  average  composition  is  pretty  con- 
stantly maintained. 

The  chyle,  or  lymph  of  digestion,  absorbs  nutrient  materials 
(mostly  fat)  from  the  intestines  and  pours  this  food  into  the  blood 
current,  to  be  distributed  to  all  parts  of  the  body. 

1  See  page  12. 


168 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  IX 


Vascular  System 


Circulating 
Fluids 

Systems 


Blood 


Description 


Functions 


Composition 


with 


SUMMARY 

r  Blood. 

I  Lymph. 

f  Blood  vascular. 

I  Lymph  vascular. 

~  ,      f  Bright  red  in  arteries. 
Color 

[  Dark  red  in  veins. 

Sticky  fluid. 

Specific  gravity,  about  1.055. 

Alkaline    reaction    when    tested 

litmus. 

Temperature,  100°  F. 
Peculiar  odor.     Salty  taste. 
^  of  the  body  weight. 
Serves  as  a  medium  for  the  interchange 

of  gases. 
Serves  as  a  medium  for  the  interchange 

of  nutritive  and  waste  materials. 
Serves  as  a  medium  for  the  transmission 

of  internal  secretions. 
Aids  in  equalizing  the  temperature  of 

the  body. 
Aids  in  protecting  the  body  from  toxic 

substances. 
Cells  f  Red,  or  erythrocytes. 

(minute,  solid  <  White,  or  leucocytes. 


particles) 

Plasma, 

transparent, 
slightly 
yellowish 
fluid. 


[  Blood-plates. 
Water,  90%. 
Proteins. 
Extractives. 
Inorganic  salts. 
Gases. 

Internal  secretions. 
Enzymes. 
Special  substances. 


Red  Cells 


Description 


Number 


Biconcave  discs 


in.  in  diameter. 


Packets  of  hemoglobin  { 


Have  no  nuclei. 

Soft,  flexible,  and  elastic. 

Cubic  milli- 

metre   of 

blood 


[  Protein. 


5,000,000  for  men. 
4,500,000  for  women. 


Number  varies,  even  in  health. 
Pathological  conditions  may  cause  decrease. 


CHAP.  IX] 


SUMMARY 


169 


Red  Cells 


Function 


Life  Cycle 


Description 


Number 


Varieties 


Functions 


Life  Cycle 


Oxygen  carriers. 

Color  due  to  oxygen  in  combination  with  haemo- 
globin. 

Originate  in  red  marrow  of  bones. 

Lose  their  nuclei  before  being  forced  into  the 
circulation,  which  suggests  that  their  term 
of  existence  is  short. 

f  Liver. 

Disintegrate  probably  in  |  Spleen. 

[  Lymph  nodes. 


Typical 
cells 


Masses  of  protoplasm. 

Nucleus  (sometimes  two  or  three 

nuclei) . 
No  cell-wall. 
Variable  in  size,  but  larger  than 

red  cells. 
5000  to  7000. 

Marked  increase  =  leucocytosis. 
Marked  decrease  =  leucopenia. 


Cubic  milli- 
metre of 
blood 

1.  Lymphocytes. 

2.  Mononuclear  leucocytes. 

3.  Polynuclear  leucocytes. 

4.  Eosinophile  leucocytes. 

5.  Mast  cells. 

1    Protective  f  (°°  By    contributing    to    the 

J- .     JT1  Ul/cL- 1/1 V  t/    I  /»  ,  •  p  j  «i         i  • 

j         formation  of  antibodies. 
[  (6)   By  process  of  phagocytosis. 

2.  Aid  in  absorption  of  fats  and  proteins. 

3.  Assist  in  clotting  of  blood. 

New  leucocytes  formed  in  lymph  nodes   and 
spleen. 

(1)  Battles  against  bacteria. 

(2)  Hemorrhage. 

(3)  Formation    of    granula- 
tion tissue. 


Numbers  lost  in 


f  Irritation  resulting  from  injury  or  infection. 
Engorgement  of  blood-vessels. 
Migration  of  .white  blood-cells. 
Diapedesis  of  red  blood-cells. 
Exudation  of  plasma. 
f  Pain. 
Heat. 
I  Redness. 
I  Swelling. 


Symptoms 


170 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  IX 


Inflam- 
mation 


Result 


(a)  Resolution  —  White  blood-cells  eat  up 
bacteria,  clear  up  debris,  and  return 
to  blood. 

(6)  Suppuration  --  Bacteria  destroy  white 
blood-cells  and  tissue  cells,  and  form 
pus. 

Plasma. 
Red  cells. 
White  cells. 
Tissue  cells. 


(c)  Pus  consists  of  - 


.    f  dead. 
Bacteria  \  r  . 

( living. 

Toxins      produced 
bacteria. 


by 


Dif- 
ferences 
between 
white 
and  red 
cells 


Blood- 
plates 


1.  Size  and  number. 

2.  Color. 

3.  Property  of  amoeboid  movement  and  shape. 

4.  Nucleus  or  nuclei. 

5.  Varieties. 

6.  Location  during  circulation. 

7.  Migration.     Found  in  other  fluids. 

8.  Functions. 


Description 


Plasma 


Disc-shaped  bodies,  vary  in  size,  always  smaller 

than  red  cells. 

Origin,  fate,  and  function  are  open  questions. 
May  assist  in  clotting  of  blood. 


j      obscure. 

)duces    the    fibrin    of     clotted 

Normally  present,  §.1%  to 
0.15%. 

May  be  increased  after  inges-- 
tion  of  large  amount. 

Derived  from  food. 

Amount  subject  to  wide  varia- 
tions. 

Represent  waste  products,  re- 
sult of  oxidation  of  food. 
Normally  present  in  small 
quantities. 


Water,  90%. 

Serum-albumin 

Proteins 

Paraglobulin 
Fibrinogen    pr 

blood. 

• 

Sugar 

Fats 

Extractives 

Urea 

Uric  acid 

Hippuric  acid 

Creatin 

Creatinin 

CHAP.  IX] 


SUMMARY 


171 


Inorganic 
Salts 

Chlorides 
Sulphates 
Phosphates 
Carbonates  j 

Sodium 
Calcium       < 
Magnesium 

De 
c 
a 
f 
r 

Oxygen. 

c 

Gases 

Nitrogen. 
Carbon  dioxide. 

Found  in  both 

venous  blood. 

Plasma 


arterial  and 


Enzymes 


Special 

Substances 


with 


Clotting 


from 

our  food,  and 
also        result 
from  chemical 
reactions      in 
our  bodies. 
Oxygen. 
Nitrogen. 
Carbon  dioxide.     Found  in  botl 

venous  blood. 
Internal 

Secretions  —  See  page  149. 

Substances  produced  by  living  cells 

which  act  by  catalysis. 
Antithrombin    j  function    in    connection 
Prothrombin      1      clotting  of  blood. 
Epinephrin  —  active  principle  of  internal  secf e- 

tion  of  adrenal  glands. 
Antigens  —  substances     which     stimulate    the 

tissues  to  form  antibodies. 

Antibodies  —  defensive     substances    found    in 
the  blood. 

Water. 
Mineral  salts. 
White  cells. 
Albumin. 

Fibrin  formed  from  fibrinogen. 
Cells,  red  and  white. 
Cellular  elements  of  blood  and 
tissues  — >  thromboplastic  sub- 
stance. 

Thromboplastic    substance    neu- 
tralizes antithrombin. 
Prothrombin + calcium  —>  throm- 

bin. 

Thrombin+ fibrinogen  — >  clot. 
Checks  hemorrhage. 

Condition  of  blood  that  lacks  clotting  power. 
(  A  temperature  higher  than  that  of  body. 
Contact  with  any  rough  surfaces. 
Contact  with  foreign  substances. 
Injury  to  the  walls  of  the  vessels. 
.  Rest. 

{A  very  low  temperature. 
Contact  with  lining  of  the  heart  and  blood- 
vessels. 


Description 


Serum 


Clot 


Process  < 


Value      . 
Hemophilia 


Hastened  by 


172 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  IX 


Clotting     .     .  \  Hindered  by 


Regeneration 
of  blood  after 
hemorrhage 


Intravenous 
Infusion 


Addition  of  strong  acids,  alkalies,  neutral 

salts,  oils,  certain  ferments,  water. 
Absence  of  calcium  salts. 
Absence  of  fibrinogen. 
Removal  of  fibrin.     (Defibrinated  blood.) 

Circulating  blood  contains  antithrombin. 


Injury  to  internal  coat  of  blood-vessels. 
Any  foreign  material   that  will   stimulate 

clotting. 
Name  given  to  clot  which  forms  inside 

vessel. 
A  thrombus  that  has  become   dislodged 

from  place  of  formation. 
[  If  immediate  ill  effects  are  counteracted  by  intravenous 
infusion,  plasma  is  regenerated  rapidly,  red  cells  within 
a  few  days  or  weeks. 


Theory  to 
account  for 

rare  occur- 

rence 

Intravascular 
Clotting 

Causes  .     . 

Thrombus 


Embolus 


Lymph 


Definition 


Benefits 


Description 


Sources   . 


Function . 


Chyle  .     .     . 


Injection  of  physiological  saline  solution 
directly  into  vein. 

1.  Heart  stimulant. 

2.  Increases  volume  of  circulating  fluid. 

3.  Red  cells  kept  circulating,  and  oxygen 

supply  kept  up  as  far  as  possible. 

4.  Tissue  cells  provided  with  water. 
Colorless  liquid. 

Alkaline    reaction   when   tested   with   lit- 
mus. 

Salty  taste.     No  odor. 

Consists  of  blood  plasma  plus  leucocytes. 

Specific  gravity  about  1.015. 

Contains  a  low  content  of  proteins. 

Contains  a  high  content  of  waste  products. 

Clots  slowly,  does  not  form  a  firm  clot. 
Filtration. 

Physical  processes  of    Diffusion. 
Osmosis. 

Active  secretory   process  on  part  of  en- 
dothelial  cells. 

Lymph   acts   as  middleman  between   the 
blood  and  the  tissues. 

Carries  nourishment  from  blood  to  tissues. 

Carries  waste  from  tissues  to  blood. 

Dependent  upon  osmosis  and  dialysis. 

Lymph  plus  nutrient  material,  mostly  fats. 


CHAPTER  X 

THE   BLOOD   VASCULAR   SYSTEM,    AND   THE   LYMPH   VASCULAR 

SYSTEM 

BLOOD  VASCULAR  SYSTEM 

THE  blood  is  the  internal  medium  on  which  the  cells  live.  It 
is  contained  in  branched  tubes  named  blood-vessels.  It  is  driven 
along  these  tubes  by  the  action  of  the  heart,  which  is  a  hollow  mus- 
cular organ  placed  in  the  centre  of  the  vascular  system.  One  set 
of  vessels  —  the  arteries  —  conducts  the  blood  out  from  the  heart 
and  distributes  it  to  the  different  parts  of  the  body,  whilst  other 
vessels  —  the  wins  —  bring  it  back  to  the  heart  again.  The 
blood  from  the  arteries  gets  into  the  veins  by  passing  through  a 
network  of  fine  tubes  which  connect  the  two,  and  which  are  named, 
on  account  of  their  small  size,  the  capillary  (i.e.,  hair-like)  vessels. 

f  Heart. 

Blood  Vascular  I  Arteries  —  small  arteries  are  named  arterioles. 
System  |  Capillaries. 

Veins  —  small  veins  are  named  venules. 


HEART 

The  heart  is  a  hollow,  muscular  organ,  situated  in  the  thorax 
between  the  lungs,  and  above  the  central  depression  of  the  dia- 
phragm. It  is  about  the  size  of  the  closed  fist,  shaped  like  a  blunt 
cone,  and  so  suspended  by  the  great  vessels  that  the  broader  end 
or  base  is  directed  upward,  backward,  and  to  the  right.  The 
pointed  end  or  apex  points  downward,  forward,  and  to  the  left. 
As  placed  in  the  body,  it  has  a  very  oblique  position,  and  the  right 
side  is  almost  in  front  of  the  left.  The  impulse  of  the  heart  against 
the  chest  wall  is  felt  in  the  space  between  the  fifth  and  sixth  ribs, 
a  little  below  and  to  the  inner  side  of  the  left  nipple. 

173 


174 


ANATOMY  AND  PHYSIOLOGY         [CHAP.  X 


FIG.  105.  —  HEART  in  situ  (Dalton,  in  Flint,  "On  the  Heart").  1,  2,  3,  4,  5, 
intercostal  spaces  ;  vertical  line,  median  line  ;  triangle,  superficial  cardiac  region  ; 
X  on  the  fourth  rib,  nipple. 


Myocardium. 


The  main  substance  of  the  heart  is  composed  of 
muscular  tissue  and  is 
called  myocardium.  (See 
page  100.) 

The  arrangement  of  the 
muscles  is  very  intricate  ; 
they  run  transversely,  lon- 
gitudinally, obliquely,  and 
in  the  apex  take  a  spiral 
turn  or  twist.  Between 
the  muscles  is  a  certain 
amount  of  reticular  tissue, 
with  numerous  blood-ves- 
sels and  lymphatics,  and, 
in  some  parts,  nerves  and 
ganglia.  There  is  also  a 
considerable  amount  of 
£atj  couecte(i  chiefly  at 

^    base    of     the     heart, 


FIG.    106.  -  ANTERIOR   VIEW   OF   HEART, 
DISSECTED,    AFTER   LONG    BOILING,   TO   SHOW 

THE  SUPERFICIAL  MUSCLES.    (Quain.) 


beneath  the  pericardium. 


CHAP.  X] 


THE  HEART 


175 


Pericardium.  —  The  heart  is  covered  by  a  membranous  sac 
called  the  pericardium  (around  the  heart).  It  consists  of  two 
parts :  (1)  an  external  fibrous  portion,  and  (2)  an  internal  serous 
portion. 

(1)  The  external  fibrous  pericardium  is  composed  of  white 
fibrous  tissue,  and  is  attached  by  its  upper  surface  to  the  large 


BRONCHIAL 
TUBES 


FIG.  107.  —  THE  PULMONARY  ARTERY  AND  AORTA.  The  front  part  of  the  right 
lung  has  been  removed,  and  the  pulmonary  vessels  and  the  bronchial  tubes  are 
thus  exposed.  Note  the  artery  marked  "brach.-ceph."  It  is  also  named  the 
innominate.  (See  page  203.)  (Gerrish.) 

blood-vessels  which  emerge  from  the  heart.  It  covers  these 
vessels  for  about  an  inch  and  a  half  (3.8  cm.)  and  blends  with  their 
sheaths.  The  lower  border  is  firmly  adherent  to  the  diaphragm, 
and  the  front  surface  is  attached  to  the  sternum  by  means  of 
fibrous  bands. 

(2)  The  internal  or  serous  portion  of  the  pericardium  is  a 
completely  closed  sac ;  it  envelops  the  heart  and  lines  the  fibrous 


176  ANATOMY  AND   PHYSIOLOGY          [CHAP.  X 

pericardium.  The  heart,  however,  is  not  within  the  cavity  of 
the  closed  sac.  (See  Fig.  108.)  That  portion  of  the  serous  peri- 
cardium which  lines  and  is  closely  adherent  to  the  heart  is  called 

the  visceral  portion  (viscus, 
organ)  ;  the  remaining  part 
of  the  serous  pericardium, 
namely,  that  which  lines 
the  fibrous  pericardium,  is 
known  as  the  parietal  por- 
tion (paries,  a  wall) .  The 
cavity  of  the  serous  peri- 

FIG.   108.  —  DIAGRAM    OF   THE    HEART  AND  ,.  .  .. 

SEROUS    PERICARDIUM.       A  shows   heart   and  CardlUHl   Contains   a   Small 

pericardium   lying   separately        B  shows   the  quantity  of   SCrOUS  liquid, 

pericardium  invagmated  by  the  heart.      V.  P.  ^ 

shows  visceral  layer  that  clings  close  to  the  heart  Its    Opposed    SUrf  aCCS    are 

muscle.      P.  P.  shows  parietal  layer  that  lines  •>•        i  •>  IJ.IT  i 

the    fibrous    pericardium.       P.  C,    pericardial  &***  by  endothelmm   and 

cavity  which  in  actual  conditions  is  a  very  nar-  are  very  smooth  and 
row  space  filled  with  pericardial  fluid. 

polished. 

As  the  opposing  surfaces,  owing  to  the  constant  contractions 
of  the  heart,  are  continually  sliding  one  upon  the  other,  they  are 
admirably  constructed  to  protect  the  heart  from  any  loss  of  power 
by  friction. 

Endocardium.  —  The  interior  of  the  heart  is  lined  by  a  smooth, 
delicate  membrane,  called  the  endocardium.  This  pavement 
membrane  (endothelium)  lines  all  the  cavities  of  the  heart,  and  is 
continued  into  the  blood-vessels,  forming  their  innermost  coat. 

The  cavities  of  the  heart.  —  The  heart  is  divided  from  the  base 
to  the  apex,  by  a  fixed  partition,  into  a  right  and  left  half,  fre- 
quently called  right  and  left  heart.  The  two  sides  of  the  heart 
have  no  communication  with  each  other  after  birth.  The  right  side 
always  contains  venous,  and  the  left  side  arterial,  blood.  Each 
half  is  subdivided  into  two  cavities,  the  upper,  called  auricle 
(atrium) ;  the  lower,  ventricle  (ventriculum) .  If  we  examine 
these  cavities,  we  notice  that  the  muscular  walls  of  the  auricles 
are  much  thinner  than  those  of  the  ventricles,  and  the  wall  of  the 
left  ventricle  is  thicker  than  that  of  the  right  (the  proportion 
being  as  3  to  1).  This  difference  in  bulk  is  to  be  accounted  for,  as 
we  shall  see  later  on,  by  the  greater  amount  of  work  the  ventricles, 
as  compared  with  the  auricles,  have  to  do.  These  cavities  com- 
municate with  one  another  by  means  of  constricted  openings,  the 


CHAP.  X] 


THE   HEART 


177 


auriculo-ventricular  orifices,  which  are  strengthened  by  fibrous 
rings  and  protected  by  valves. 

Important  orifices  of  the  heart.  —  Eight  large  blood-vessels 
are  connected  with  the  heart.  These  eight  orifices  plus  the  two 
between  the  auricles  and  ventricles,  make  a  total  of  ten. 


RIGHT    PULMO 
NARY    VEINS 


1  Left  pulmonary 
veins 


Left  auricular 
appendix 


Anterior  coro- 
nary vessels 
Dart  pointing  to 
aortic  opening 


Cavity  of  left 
ventricle 


Base  of  anterior 
columna?  carnese 


(Anterior  columnse 
carnese  cut  in  two 
and  lifted  up  and 
back 


External  flap  of 
mitral  valve 


FIG.  109.  —  LEFT  AURICLE  AND  VENTRICLE,  THE  HIND  WALL  OF  EACH  HAVING 
BEEN  REMOVED.  The  columnae  carneae  are  muscle  columns  which  project  from 
nearly  the  whole  of  the  inner  surface  of  the  ventricles.  Some  of  them  give  origin  to 
the  papillary  muscles.  (Gerrish.) 


On  the  right  side  of  the  heart,  the  superior  and  inferior  vena 
cava  empty  into  the  auricle,  and  the  pulmonary  artery  leaves  the 
ventricle. 

On  the  left  side  of  the  heart,  four  pulmonary  veins  empty  into 
the  auricle,  and  the  aorta  leaves  the  ventricle.  There  are  some 
smaller  openings  to  receive  blood  directly  from  the  heart  sub- 
stance, and  before  birth  there  is  an  opening  between  the  right  and 


178 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  X 


left  auricle  called  the  foramen  ovale.     Normally  this  closes  as  soon 
as  the  infant  breathes. 

Valves  of  the  heart.  —  The  auriculo-ventricular  orifices  and  the 
openings  into  the  aorta  and  pulmonary  artery  are  guarded  by 

valves. 

The  tricuspid  valve.  — 
The  valve  guarding  the 
right  auriculo-ventricular 
opening  is  composed  of 
three  irregular-shaped 
flaps,  or  cusps,  and  hence 
is  named  tricuspid.  The 
flaps  are  mainly  formed 
of  fibrous  tissue  covered 
by  endocardium.  At  their 
bases  they  are  continuous 
with  one  another,  and  form  a  ring-shaped  membrane  around  the 
margin  of  the  auricular  opening :  their  pointed  ends  are  directed 
downward,  and  are  attached  by  cords,  the  chordce  tendinece,  to 


FIG.  110.  —  CROSS-SECTION  THROUGH  BOTH 
VENTRICLES,  SHOWING  THE  SHAPE  or  THEIR 
CAVITIES  AND  THE  RELATIVE  THICKNESS  OF 
THEIR  WALLS.  (Gerrish.) 


FIG.  111.  —  VALVES  OP  THE  HEART  AND  GREAT  ARTERIES,  VIEWED  FROM  ABOVE, 
THE  AURICLES  HAVING  BEEN  REMOVED.     (Gerrish.) 

little  muscular  pillars,  the  papillary  muscles,  provided  in  the  in- 
terior of  the  ventricles  for  this  purpose. 

The  bicuspid  valve.  —  The  valve  guarding  the    left    auricular 
opening  consists  of  only  two  flaps  or  cusps,  and  is  named  the  bi- 


CHAP.  X]  .          THE   HEART  179 

cuspid,  or  mitral  valve.  It  is  attached  in  the  same  manner  as 
the  tricuspid  valve,  which  it  closely  resembles  in  structure,  except 
that  it  is  much  stronger  and  thicker  in  all  its  parts. 

Function.  —  These  valves  oppose  no  obstacle  to  the  passage  of 
the  blood  from  the  auricles  into  the  ventricles  because  the  free 
edges  of  the  flaps  are  pointed  in  the  direction  of  the  blood  cur- 
rent ;  but  any  flow  forced  backward  gets  between  the  flaps  and 
the  wall  of  the  ventricle,  and  drives  the  flaps  upward,  until, 
meeting  at  their  edges,  they  unite  and  form  a  complete  transverse 
partition  between  the  ventricle  and  auricle.  Being  retained  by 
the  chordse  tendinese,  the  expanded  flaps  of  the  valve  resist  any 
pressure  of  the  blood  which  might  otherwise  force  them  to  open  into 
the  auricle ;  at  the  same  time  the  papillary  muscles,  to  which  the 
chordae  tendinese  are  attached,  contract  and  shorten  and  thus  keep 
them  taut. 

Semilunar  valves.  —  The  valves  between  the  ventricles  and 
arteries  are  called  the  semilunar  valves  (aortic  and  pulmonary). 

OPENING   OF   RIGHT          SINUS   OF     1  OPENING    OF    LEFT 

CORONARY  ARTERY  VALSALVA    /|\  CORONARY    ARTERY 


=  _  (LEFT  POSTERIOR 

ANTERIOR:  <"^W^      \  •    SEGMENT 

SEGMENT   CORPUS/  R|QHT  FIBROUS  THICKEN- 

1        POSTERIOR  ING   OF  EDGE 

SEGMENT 

FIG.   112.  —  AORTIC  VALVE.     The  artery  has  been  cut  open  between  the  anterior 
and  left  posterior  segments,  and  spread  out.     (Gerrish.) 

These  valves  consist  of  three  half-moon-shaped  pockets,  each 
pocket  being  attached  by  its  convex  border  to  the  inside  of  the 
artery  where  it  joins  the  ventricle,  while  its  other  border  projects 
into  the  interior  of  the  vessel.  Small  nodular  bodies,  called  the 
corpora  Arantii,  are  attached  to  the  centre  of  the  free  edge  of  each 
pocket. 

Function.  —  These  valves  offer  no  resistance  to  the  passage  of 


180 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  X 


blood  from  the  heart  into  the  arteries,  as  the  free  borders  project 
into  the  arteries,  but  they  form  a  complete  barrier  to  the  passage 
of  blood  in  the  opposite  direction.  In  this  case  each  pocket 
becomes  filled  with  blood,  and  the  free  borders  are  floated  out  and 
distended  so  that  they  meet  in  the  centre  of  the  vessel.  The 
corpora  Arantii  assist  in  the  closure  of  these  valves  and  help  to 
make  the  barrier  perfect. 

The  orifices  of  the  heart  which  open  into  veins  are  not  pro- 
tected by  valves,  with  the  possible  exception  of  the  opening 
into  the  inferior  vena  cava  which  is  partly  covered  by  a  mem- 
brane known  as  the  Eustachian  valve. 

Auriculo- ventricular  bundle  of  His.  The  muscular  tissue  of 
the  auricles  is  not  continuous  with  that  of  the  ventricles.  They 

SUPERIOR  VENA  CAVA 

SINO-AURICULAR  NODE 

AURICULO- VENTRICULAR  NODE 

.PULMONARr 
VEINS 


LEFT    AURICLE 
BUNDLE  OF  HIS 


MITRAL  VALVE 


LEFT  VENTRICLE 


RIGHT 
VENTRICLE 


FIG.  113.  —  DIAGRAM  OF  THE  AURICULO-VENTRICULAR  NODE  AND  BUNDLE  OF  His. 

are  connected  by  fibrous  tissue  and  the  auriculo-ventricular 
bundle  of  His,  which  consists  of  muscular  and  nervous  tissue. 
This  bundle  arises  in  a  collection  of  cells  known  as  the  auriculo- 
ventricular  node,  located  in  the  septum  between  the  auricles.  It  is 
connected  with  the  muscles  of  the  auricles  and  also  with  the 
remnant  of  sinus  tissue  —  the  sino-auricular  node  —  which  is 
located  at  the  mouth  of  the  superior  vena  cava.1  It  passes  down 

1  See  page  217. 


CHAP.  X]  ARTERIES  181 

the  septum  between  the  auricles  to  the  septum  between  the 
ventricles,  where  it  divides  into  right  and  left  bundles,  one  for  each 
ventricle.  In  the  lower  part  of  the  ventricles  each  bundle  sepa- 
rates into  numerous  strands  which  spread  over  the  entire  internal 
surface.  The  terminal  strands  are  called  Purkinje  fibres.  The 
significance  of  these  structures  is  discussed  on  page  230. 

Blood  supply.  —  Just  after  the  aorta  leaves  the  left  ventricle  it 
gives  off  two  small  branches,  called  the  right  and  left  coronary 
arteries.  They  encircle  the  heart  like  a  crown,  hence  their  name. 
They  supply  the  substance  of  the  heart  with  blood,  as  the  blood 
contained  within  the  cavities  of  the  heart  only  nourishes  the 
endocardium. 

Nerve  supply.  — The  heart  is  supplied  (1)  by  the  vagi  nerves 
from  the  central  nervous  system  and  (2)  by  nerves  from  the 
sympathetic  system.  Stimulation  of  the  vagi  fibres  slows  the 
action  of  the  heart.  They  are  therefore  known  as  cardiac  in- 
hibitors. Stimulation  of  the  sympathetic  nerves  increases  the 
force  of  the  heart  beat,  therefore  they  are  known  as  cardiac 
accelerators. 

ARTERIES 

The  arteries  are  tubes  that  carry  blood  from  the  heart  and  are 
composed  of  three  coats  :  — 

1 .  —  An  inner  endothelial  lining  which  is  continuous  with  the 
endothelium   lining  the  heart.     It  furnishes  a  smooth,  slippery 
surface  over  which  the  blood  can  flow  without  friction. 

2.  —  A   middle    coat 
of  fibrous  elastic  tissue 
with  muscles  interlaced 
and  circularly  disposed 
around  the  vessel.     By 
virtue  of  the  structure 
of  the  middle  coat,  the 
arteries    are    both    ex- 
tensile and  elastic.*      Jt  FIG.  114.- DIAGRAM  OF  A  CROSS-SECTION  OF 

AN  ARTERY,  SHOWING  THE  COMPOSITION  OF  ITS 

is  thicker  and  contains     TUNICS.    (Gerrish.) 

1  It  is  well  to  bear  in  mind  the  difference  between  extensile  and  elastic.  By 
extensile  we  mean  that  an  object  can  be  stretched  ;  by  elastic  that  it  returns  to  its 
former  shape  as  soon  as  the  stretching  force  is  removed. 


182  ANATOMY  AND   PHYSIOLOGY          [CHAP.  X 

a  larger  proportion  of  elastic  tissue  in  the  larger  arteries.  In  the 
smaller  arteries  it  is  thinner  and  contains  a  larger  proportion  of 
muscular  tissue.  The  proper  functioning  of  the  arteries  depends 
upon  their  extensibility  and  elasticity  and  may  be  demonstrated 
by  the  following  example  :  — 

If  we  tie  a  piece  of  a  large  artery  at  one  end  and  inject  fluid 
into  the  other  end,  the  artery  swells  out  to  a  very  great  extent, 
but  will  return  at  once  to  its  former  size  when  the  fluid  is  let  out. 

The  great  extensibility  and  elasticity  of  the  arteries  adapts 
them  for  receiving  the  additional  amount  of  blood  thrown  into 
them  at  each  contraction  of  the  heart. 

3.  —  An  outer,  dense  fibrous  coat  with  fibres  arranged  longi- 
tudinally. The  strength  of  an  artery  depends  largely  upon  the 
outer  fibrous  coat ;  it  is  far  less  easily  cut  or  torn  than  the  other 
coats,  and  serves  to  resist  undue  expansion  of  the  vessel. 

The  arteries  do  not  collapse  when  empty,  and  when  an  artery  is 
severed  the  orifice  remains  open.  The  muscular  coat,  however, 
contracts  somewhat  in  the  neighborhood  of  the  opening,  and  the 
elastic  fibres  cause  the  artery  to  retract  a  little  within  its  sheath, 
so  as  to  diminish  its  caliber  and  permit  a  blood-clot  to  plug  the 
orifice.  This  property  of  the  severed  artery  is  an  important 
factor  in  the  arrest  of  hemorrhage. 

Blood  and  nerve  supply  of  the  arteries.  —  The  blood  which 
flows  through  the  arteries  nourishes  only  the  inner  coat.  The 
middle  and  outer  coats  are  supplied  with  arteries,  capillaries,  and 
veins,  called  vasa  vasorum,  or  blood-vessels  of  the  blood-vessels. 

The  muscular  tissue  found  in  the  walls  of  the  arteries  is  supplied 
with  nerves  chiefly  from  the  sympathetic  system.  These  nerves 
are  called  vasomotor,  and  are  divided  into  two  sets,  (1)  vaso- 
constrictor, and  (2)  vaso-dilator. 

Stimulation  of  one  set  of  these  nerves  (vaso-constrictor)  causes 
contraction  of  the  muscles  and  constriction  of  the  arteries ;  stimu- 
lation of  a  second  set  (vaso-dilator)  causes  a  relaxation  of  the 
muscles,  and  dilatation  of  the  arteries.  The  widening  and  nar- 
rowing of  the  arteries  not  only  affects  the  local  circulation  in 
different  parts  of  the  body,  but  the  amount  of  resistance  they 
oppose  to  the  arterial  impulse  also  influences  in  some  degree  the 
character  of  the  heart-beat.  The  term  "  tone  of  the  arteries  "  is 
used  to  express  the  normal  degree  of  contracture  of  the  arterial 


CHAP.  X] 


CAPILLARIES 


183 


walls.  This  is  an  inherent  property  which  is  independent  of  the 
nervous  system. 

Sheaths  of  the  arteries.  —  The  greater  number  of  the  arteries 
are  accompanied  by  a  nerve  and  one  or  two  veins  and  surrounded 
by  a  sheath  of  connective  tissue,  which  helps  to  support  and  hold 
these  structures  in  position. 

Size  of  the  arteries.  —  The  largest  arteries  in  the  body,  the 
aorta  and  pulmonary  artery,  measure  about  one  inch  (2.8  cm.)  in 
diameter,  at  their  connection  with  the  heart.  These  arteries 
give  off  branches,  which  divide  and  subdivide  into  smaller  branches. 
A  branch  of  an  artery  is  always  less  than  the  trunk  from  which  it 
springs,  hence  the  arteries  grow  smaller  as  they  subdivide,  and 
gradually  lose  their  characteristic  structure.  The  smallest  arte- 
ries are  called  arterioles,  and  at  their  distal  ends,  where  only  the 
internal  coat  remains,  the  capillaries  begin. 

CAPILLARIES 

The  capillaries  are  exceedingly  minute  vessels  which  average 
about  2Too"  °f  an  mcn  (-0125  mm.)  in  diameter.  They  connect 
the  arterioles  (smallest  arteries)  with  the  venules  (smallest  veins), 
thus  receiving  the  blood  from  the  ar- 
terioles and  carrying  it  to  the  venules. 

Structure.  —  The  walls  of  the  capil- 
laries are  formed  entirely  of  one  layer 
of  simple  endothelium  composed  of 
flattened  cells  joined  edge  to  edge  by 
cement  substance,  and  continuous  with 
the  layer  which  lines  the  arteries  and 
veins. 

Distribution.  —  The  capillaries  com- 
municate freely  with  one  another  and 
form  interlacing  networks  of  variable 
form  and  size  in  the  different  tissues. 
All  the  tissues,  with  the  exception  of 
the  cartilages,  hair,  nails,  cuticle,  and 

cornea  of  the  eye,1  are  traversed  by  these  networks  of  capillary 
vessels.  Their  diameter  is  so  small  that  the  blood  cells  must  pass 


FIG.  115.  —  FINE  CAPIL- 
LARIES FROM  THE  MESENTERY. 
(Collins.) 


1  These  parts  not  penetrated  by  the  blood-vessels  imbibe  nutritive  matter  from 
adjacent  tissues,  and  are  just  as  dependent  on  the  blood  as  all  the  other  tissues. 


184 


ANATOMY  AND  PHYSIOLOGY          [CHAP.  X 


through  them  in  single  file  and  very  frequently  the  cell  is  larger 
than  the  caliber  of  the  vessel,  and  has  to  be  squeezed  to  enable  it 
to  pass  through.  In  many  parts  they  lie  so  closely  together  that 
a  pin's  point  cannot  be  inserted  between  them.  They  are  most 
abundant,  and  form  the  finest  networks,  in  those  organs  where 
the  blood  is  needed  for  purposes  other  than  local  nutrition,  as, 
for  example,  secretion  or  absorption. 

Function.  —  In  the  glandular  organs  the  capillaries  supply  the 
substances  requisite  for  secretion;  in  the  alimentary  canal  they 
take  up  some  of  the  elements  of  digested  food ;  in  the  lungs  they 
absorb  oxygen  and  give  up  carbon  dioxide ;  in  the  kidneys  they 
discharge  the  waste  products  collected  from  other  parts;  all  the 

time,  everywhere  through  their  walls, 
that  interchange  is  going  on  which  is 
essential  to  the  renovation  and  life  of 
the  whole  body.  It  is  in  the  capil- 
laries,  then,  that  the  chief  work  of 
the  blood  is  done  ;  and  the  object  of 
the  vascular  mechanism  is  to  cause 
the  blood  to  flow  through  these  ves- 
sels in  the  manner  best  adapted  for 
accomplishing  this  work. 

VEINS 

The  veins  are  tubes  that  carry 
blood  to  the  heart.  They  have  three 
coats  and  on  the  whole  resemble  the 
arteries  in  structure.  They  differ 
from  them  in  having  :  (1)  much  thin- 
ner walls  (see  Fig.  116) ;  (2)  they 
contain  less  elastic  tissue,  more  white 
fibrous  tissue,  and  because  of  this 
are  not  so  elastic  or  contractile  as  the 
arteries;  (3)  many  of  the  veins  are 
provided  with  valves. 
Valves.  —  The  valves  are  semilunar  folds  of  the  internal  coat  of 

the  veins ;  and  usually  consist  of  two  flaps,  rarely  one  or  three. 
The  convex  border  is  attached  to  the  side  of  the  vein,  and  the 

free  edge  points  toward  the  heart.     Their  function  is  to  prevent 


FIG.   116.  —  TRANSVERSE  SEC- 
TION THROUGH  A   SMALL  ARTERY 

AND  VEIN,  SHOWING  THE  RELA- 
TIVE DIFFERENCE  IN  THE  THICK- 
NESS OF  THEIR  WALLS.  In  the 
vein  (V}  the  outer  coat  is  thickest, 
in  the  artery  (A)  the  extensile 
and  elastic  middle  coat  is  thickest. 
(Klein  and  Noble  Smith.) 


CHAP.  X] 


LYMPH   VASCULAR  SYSTEM 


185 


regurgitation  and  keep  the  blood  flowing  in  the  right  direction,  i.e., 
toward  the  heart. 

If  for  any  reason  the  blood  on  its  onward  course  toward  the 
heart  is  driven  backward,  the  refluent  blood,  getting  between  the 
wall  of  the  vein  and  the  flaps  of  the  valve,  will  press  them  inward 
until  their  edges  meet  in  the  middle  of  the 
channel  and  close  it. 

The  valves  are  most  numerous  in  the 
veins  where  regurgitation  is  most  likely  to 
occur,  i.e.,  the  veins  of  the  extremities.  For 
the  same  reason  a  greater  number  are  found 
in  the  lower  than  in  the  upper  limbs.  They 
are  absent  in  many  of  the  small  veins,  in 
the  large  veins  of  the  trunk,  and  in  veins 
not  subjected  to  muscular  pressure.  The 
veins,  like  the  arteries,  are  supplied  with 
both  blood-vessels  and  nerves ;  the  supply, 
however,  is  far  less  abundant. 

It  must  be  remembered  that  although  the 
arteries,  capillaries,  and  veins  have  each  the 
distinctive  structure  above  described,  it  is  at  the  same  time  diffi- 
cult to  draw  the  line  between  the  arteriole  and  large  capillary ;  and 
between  the  large  capillary  and  venule.  The  veins  on  leaving  the 
capillary  networks  only  gradually  assume  their  several  coats,  while 
the  arteries  dispense  with  their  coats  in  the  same  imperceptible 
way  as  they  approach  the  capillaries. 

LYMPH  VASCULAR  SYSTEM 

As  the  process  of  lymph  formation  is  continual,1  it  follows  that 
oedema  would  result  from  the  accumulation  of  lymph  if  some 
system  of  drainage  were  not  provided  to  return  the  lymph  to  the 
blood.  This  drainage  system  is  called  the  lymph  vascular  system. 
Lymph  spaces 

Lymph  capillaries. 
Lymphatics. 
Thoracic  duct. 
Right  lymphatic  duct. 


FIG.  117.  —  DIAGRAM 
SHOWING  VALVES  OF 
VEINS.  A,  part  of  a  vein, 
laid  open,  with  two  pairs 
of  valves  ;  B,  longitudi- 
nal section  of  vein,  show- 
ing valves  closed.  (Shar- 
pey.) 


Lymph  Vascular 
System 


Lymph  vessels 


Lacteals. 
Serous  cavities. 


Lymph  nodes 

1  See  page  166. 


FIG.  118.  —  THE  REGIONS  WHOSE  LYMPH  FLOWS  INTO  THE  RIGHT  LYMPHATIC 
DUCT  ARE  SUGGESTED  BY  THE  RED  AREA  ;  THOSE  WHICH  ARE  TRIBUTARY  TO  THE 
THORACIC  DUCT  BY  THE  BLUE  AREA.  (Gerrish.) 

186 


CHAP.  X] 


LYMPH   VASCULAR   SYSTEM 


187 


Lymph  spaces.  —  The  microscopic  spaces  which  exist  between 
the  cells  are  always  filled  with  lymph  and  are  called  lymph  spaces. 
In  them  the  lymphatics  begin. 

Lymph  vessels.  —  The  plan  upon  which  the  lymphatic  system 
is  constructed  is  similar  to  that  of  the  blood  vascular  system, 
if  we  omit  the  heart  and  the  arteries.  In  the  lymph  spaces  we 
find  the  closed  ends  of  minute  microscopic  vessels,  called  lymph 
capillaries,  which  are  comparable  to,  and  often  larger  than,  the 
blood  capillaries.  These  lymph  capillaries  unite  to  form  larger 
vessels  called  lymphatics,  which  are  comparable  to 
the  veins.  The  lymphatics  continue  to  unite  and 
form  larger  and  larger  vessels  until  finally  they  con- 
verge into  two  main  channels,  (1)  the  thoracic  duct, 
and  (2)  the  right  lymphatic  duct. 

The  thoracic  duct.  —  The  thoracic  duct  begins 
at  the  second  lumbar  vertebra  and  ascends  upward 
to  the  seventh  cervical.  It  lies  in  front  of  the 
bodies  of  the  vertebrse,  gradually  inclining  towards 
the  left,  until,  on  a  level  with  the  seventh  cervical 
vertebra,  it  turns  outward  and  arches  downward 
and  forward  to  terminate  in  the  innominate  vein 
at  the  point  of  junction  of  the  left  internal  jugular 
and  left  subclavian. 

It  is  from  fifteen  to  eighteen  inches  (38-45  cm.) 
long  in  the  adult,  and  is  about  the  size  of  a  goose 
quill.  It  receives  the  lymph  from  the  left  side  of 
the  head,  neck,  and  chest,  all  of  the  abdomen  and 
both  lower  limbs,  also  the  chyle  from  the  lacteals. 
It  is  dilated  below,  where  it  receives  the  lymph 
from  the  lower  limbs  and  the  chyle  from  the  lac- 
teals,  the  dilatation  being  known  as  the  chyle  cistern  (recep- 
taculum  chyli).  (See  Fig.  145.) 

The  right  lymphatic  duct.  —  The  right  lymphatic  duct  is  a 
short  vessel,  usually  from  one-half  to  one  inch  (1.3  to  2.5  cm.)  in 
length.  It  pours  its  contents  into  the  innominate  vein  at  the 
junction  of  the  right  internal  jugular  and  subclavian  veins. 

The  lymphatics  from  the  right  side  of  the  head,  neck,  the  right 
arm,  and  the  upper  part  of  the  trunk  enter  the  right  lymphatic 
duct.  The  parts  drained  by  each  are  suggested  by  Fig.  118. 


FIG.  119.— 
VALVES  OF  THE 
LYMPHATICS. 


188 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  X 


Structure  of  the  lymph  vessels.  —  The  lymphatics  resemble  the 
veins  in  their  structure  as  well  as  in  their  arrangement.  The 
smallest  have  but  a  single  coat  of  endothelioid  cells,  having  a 
peculiar  dentated  outline.  The  larger  vessels  have  three  coats, 

similar  to  veins,  except  that 
they  are  so  thin  as  to  be  trans- 
parent, and  are  more  abun- 
dantly supplied  with  valves. 
The  valves  are  constructed  and 
arranged  in  the  same  fashion 
as  those  of  the  veins,  but  fol- 
low one  another  at  such  short 
intervals  that,  when  distended, 
they  give  the  vessel  a  beaded 
or  jointed  appearance.  They 
are  usually  wanting  in  the 
smaller  networks.  The  valves 
allow  the  passage  of  material 
from  the  smaller  to  the  larger 
lymphatics,  and  from  these  into 
the  veins,  but  obstruct  the  flow 
in  the  opposite  direction. 
Classification  of  lymphatics. 
-The  lymph,  like  the  blood 
in  the  veins, 'is  returned  from 
the  limbs  and  viscera  by  a 
superficial  and  a  deep  set  of 
vessels.  The  superficial  lym- 
phatic vessels  are  placed  im- 
mediately beneath  the  skin, 
and  accompany  the  superficial 
veins.  In  the  interior  of  the 
body  the  lymphatics  lie  in  the 
submucous  tissue  throughout  the  whole  length  of  the  gastro 
pulmonary  and  genito-urinary  tracts,  and  in  the  subserous  tissue 
of  the  thoracic  and  abdominal  cavities.  The  deep  lymphatics, 
fewer  in  number  and  larger  than  the  superficial,  accompany  the 
deep  blood-vessels. 

Lacteals.  —  The  lymphatics  that  have  their  origin  in  the  villi 


FIG.  120.  —  LACTEALS  AND  LYMPHATICS, 
DURING  DIGESTION.     (Dalton.) 


CHAP.  X] 


LYMPH   VASCULAR  SYSTEM 


189 


of  the  small  intestine  are  called  lacteals.  During  the  period  of 
intestinal  digestion  they  are  filled  with  chyle,  which  has  a  white 
aspect,  due  to  fat  absorbed  from  the  food,  and  suspended  in  it 
like  oil  in  milk.  After  fasting,  the  lacteals  contain  lymph  which 
differs  very  little  from  the  lymph  found  in  the  ordinary  lymphatics. 

Serous  cavities.  —  A  close  relationship  exists  between  the  lym- 
phatics and  the  serous  cavities  of  the  body,  i.e.,  pleural,  pericardial, 
and  peritoneal ;  also  the  synovial  bursae.  These  cavities  are  lined 
by  endothelium  through  which  the  lymph  transudes  by  osmosis. 

Function  of  the  lymphatics.  —  The  function  of  the  lymphatics 
is  to  carry  from  the  tissues  to  the  veins  all  the  materials  which  the 
tissues  do  not  need.  Functionally 
they  may  be  considered  between  the 
capillaries  and  the  veins,  as  they 
gather  up  the  lymph  which  exudes 
through  the  thin  capillary  walls,  and 
return  it  to  the  innominate  veins. 
Here  it  becomes  mixed  with  the  blood, 
enters  the  superior  vena  cava,  and 
then  the  right  auricle  of  the  heart. 
The  function  of  the  lacteals  is  to  help 
in  the  absorption  of  digested  food, 
especially  fats. 

Lymph  nodes. — The  lymph  nodes 
are  numerous  round  or  ovoid  bodies 
placed  in  the  course  of  the  lym- 
phatics. They  vary  in  size  from  a 
pinhead  to  an  almond.  A  lymph  node 
is  covered  by  an  envelope,  or  capsule, 
of  connective  and  muscular  tissue. 
This  capsule  sends  fibrous  bands 
called  trabeculse  (little  beams)  into 
the  substance  of  the  node,  and  di- 
vides it  into  irregular  spaces,  which  communicate  freely  with  each 
other.  The  irregular  spaces  are  occupied  by  a  mass  of  cellular 
pulp  substance,  which,  however,  does  not  quite  fill  them  as  it 
never  touches  the  capsule  or  trabeculse,  but  leaves  a  narrow  in- 
terval between  itself  and  them.  It  looks  as  if  the  pulp  had 
originally  filled  the  framework  and  then  shrunk  away  slightly  on 


FIG.  121.  —  A  LYMPH  NODE 
WITH  ITS  AFFERENT  AND  EFFER- 
ENT VESSELS.  (Gerrish.) 


190  ANATOMY  AND   PHYSIOLOGY         [CHAP.  X 


DEEP   CERVICAL    NODE 


.PROPER    AXILLARY 
NODES 


EPICONDYLAR    NODE 


'ALMAR    PLEXUS 


FIG.  122.  —  THE  LYMPH  NODES  AND  VESSELS  OF  THE  UPPER  LIMB.      (Gerrish.) 


CHAP.  X] 


LYMPH  VASCULAR  SYSTEM 


191 


all  sides.  The  spaces  thus  left  form 
channels  for  the  passage  of  the  lymph, 
which  enters  by  afferent  vessels,  and, 
after  circulating  through  the  node,  is- 
sues by  efferent  vessels.  The  substance 
of  a  lymph  node  is  reticular  adenoid 
tissue.  They  are  well  supplied  with 
blood. 

Location  of  nodes.  —  There  is  a  super- 
ficial and  a  deep  set  of  nodes,  just  as 
there  is  a  superficial  and  a  deep  set  of 
lymphatics  and  veins.  Occasionally  a 
node  exists  alone,  but  they  are  usually 
in  groups  or  chains,  and  arranged  around 
blood-vessels.  They  are  found  in  great 
numbers  in  the  neck,  thorax,  axilla, 
groin,  mesentery,  and  alongside  of  the 
aorta,  inferior  vena  cava,  and  the  iliac 
vessels.  A  few  are  found  in  the  poplit- 
eal space  and  in  the  arm  as  far  as  the 
elbow,  but  none  farther  down  the  leg  or 
forearm.  They  are  usually  named  from 
the  position  in  which  they  are  found  in 
the  body,  viz.  cervical  in  the  neck, 
thoracic  in  the  thorax,  axillary  in  the 
axilla,  inguinal  in  the  groin,  mesenteric 
in  the  mesentery. 

Function  of  the  lymph  nodes.  —  The 
lymph  nodes  serve  two  important  pur- 
poses :  — 

(1)  As  filters  for  the  lymph.  —  In  this 
way  they  act  as  safety-valves  and  serve 
to  retard  the  spread  of  infection  through 
the  body.  If  any  portion  of  the  body 
is  infected,  the  poison  may  be  carried 
by  the  lymphatics  to  their  special  nodes. 
There  its  course  is  stopped  and  the 
node  may  suffer  enlargement  or  even 
break  down  and  be  destroyed.  If  the 


FIG.  123.  — THE  LYMPH 
NODES  AND  VESSELS  OF  THE 
LOWER  LIMB.  (Gerrish.) 


192 


ANATOMY  AND   PHYSIOLOGY          [CHAP.  X 


infection  is  not  arrested,  the  node  next  in  line  will  suffer,  then  the 
next,  and  so  on. 


FIG.  124.  —  THE  LYMPH  NODES  OF  THE  NECK  AND  UPPER  PART  OF  THE  THORAX. 

(Gerrish.) 

(2)  Multiplication  of  leucocytes.  —  In  its  passage  through  the 
node  the  lymph  takes  up  fresh  leucocytes,  which  are  continually 
multiplying  by  cell  division  in  the  substance  of  the  node. 


CHAP.  X] 


SUMMARY 


193 


Blood  Vascular 
System 


Location 


Structure 


Cavities 


Orifices 


Right 
heart 


Left 
heart 


Right 
heart 


Left 
heart 


Right 
auricle 

Right  ven- 
tricle 


SUMMARY 

Heart. 

Arteries  —  small  arteries  are  named  arterioles. 

Capillaries. 

Veins  —  small  veins  are  named  venules. 

Between  lungs. 

Above  diaphragm. 

Smooth  lining  on  inside  —  Endocardium. 

Muscle  substance  —  Myocardium. 

f  Fibrous  portion. 

Outside  covering  —  Pericardium  {  a  f  Visceral. 

Serous  {  «    .  . 
[  [  Parietal. 

(  Receives  blood. 
[  Thin  walls. 
Expels  blood  into  pulmonary 

artery. 
Thick  walls. 
Left  f  Receives  blood. 

auricle     ( Thin  walls. 
Left    ven-  f  Expels  blood  into  aorta, 
tricle        [  Very  thick  walls. 

f  Superior    vena    cava  —  re- 
turns  blood   from   upper 
Right  portion  of  body, 

auricle       Inferior  vena  cava  —  returns 
blood  from  lower  portion 
I     of  body. 

Auriculo-ventricular  orifice  between  au- 
ricle and  ventricle. 

Right  ven-  f  Pulmonary  artery  —  carries 
tricle        [      blood  from  heart  to  lungs, 
f  Two  right  pulmo-  j  Return 
Left  nary  veins  blood 

auricle         Two   left  pulmo-        from 

nary  veins          J      lungs. 
Auriculo-ventricular  orifice  between  auri- 
cle and  ventricle. 

Left    ven-  f  Aorta  —  distributes  blood  to 
tricle        [      all  parts  of  body. 


194 


ANATOMY  AND  PHYSIOLOGY         [CHAP.  X 


Valves 


branches  from  aorta. 


Tricuspid  valve  —  composed  of  three  cusps  situated 

in  the  right  ventricle. 

Bicuspid  or  mitral  valve  —  composed  of  two  strong, 
thick  cusps  situated  in  the  left  ventricle. 
Function  —  Prevent  flow  of  blood  from  ventricles 
into  auricles. 

Aortic  —  composed  of  three  half-moon- 
shaped  pockets  between  aorta  and 
left  ventricle. 

Semilunar  J  Pulmonary  —  composed    of    three    half- 
valves     1      moon-shaped  pockets  between  pulmo- 
nary artery  and  right  ventricle. 
Function.  —  Prevent  flow  of  blood  from 

arteries  into  ventricles. 

Auriculo-ventricular  bundle.  —  Bundle  of  muscular  and  nervous 
tissue  located  in  septum  between  right  and  left  heart,  which  con- 
nects the  musculature  of  auricles  and  ventricles. 

Central   nervous   system.  —  Vagi   nerves,    inhibitory 

fibres,  slow  the  heart. 
Sympathetic  system.  —  Accelerator  fibres  increase 

rapidity  and  force  of  heart. 
Right  coronary  artery  1 
Left  coronary  artery    J 
Hollow  tubes  —  Carry  blood  from  heart. 

1.  Endothelial  lining. 
Coats    2.  Muscular  and  elastic  tissue. 

3.  Fibrous  tissue. 
Sheaths  —  outside  covering  of  connective  tissue  which 

surrounds  the  arteries. 

Size  —  Aorta  about  one  inch  in  diameter.  Arteries 
grow  smaller  as  they  subdivide.  Smallest 
ones  are  microscopic  and  are  called  arterioles. 

Tiny  tubes  —  about  T1foT  of  an  inch  in  diameter.     Con- 
nect arterioles  and  venules. 
One  coat  of  simple  endothelium. 
Communicate  freely  —  form  networks. 
Collapsible  tubes  —  smallest  ones,  called  venules,  begin 

where  capillaries  end. 
Carry  blood  to  heart. 
Three  coats,  same  as  arteries  but  thinner. 
Valves  —  semilunar  pockets. 
Vaso  vasorum  —  Term  applied  to  blood-vessels  that  are  supplied  to  coats 

of  other  blood-vessels. 

Vasomotor.  —  Term  applied  to  nerves  supplied  to   J  Vaso-constrictor. 
blood-vessels  1  Vaso-dilator. 


Nerve  Supply 


Blood  Supply 


Arteries  .  .  . 
Characterized 
by  elasticity 


Capillaries   .     . 
Characterized 
by  multiplic- 
ity 

Veins  .  .  .  . 
Characterized 
by  valves 


CHAP.  X] 


SUMMARY 


195 


Lymph 
Vascular 
System 


Lymph  spaces  —  Microscopic   spaces   which  exist  between 
cells  of  which  tissues  are  composed. 
Lymph  capillaries. 
Lymphatics. 
Thoracic  duct. 
Right  lymphatic  duct. 
Lacteals. 
Serous  cavities. 


Lymph  vessels 


Lymph  nodes 


Lymph 
Capillaries 

Lymphatics  — 


Lymph  Vessels 


Thoracic  Duct 


Right  Lym- 
phatic Duct 


Classification 


Lacteals 


Origin  in  lymph  spaces. 

One  coat  of  endothelium  —  dentated. 

Start  as  microscopic  lymph  capillaries, 
unite  to  form  lymphatics.  Compa- 
rable to  formation  of  veins. 

three  coats  —  numerous  valves. 

15  to  18  in.  long.     Size  of  goose-quill. 

In  front  of  vertebra  from  2d  lumbar  to 
7th  cervical. 

Has  three  coats  —  numerous  valves. 

Dilatation  at  lower  portion  called  chyle 
cistern. 

Receives  lymph  from  left  side  of  head, 
neck,  and  chest,  left  arm,  all  of  abdo- 
men, and  both  lower  limbs.  Re- 
ceives chyle  from  lacteals. 

Pours  lymph  and  chyle  into  left  in- 
nominate vein. 

|  to  1  in.  long. 

Receives  lymph  from  right  side  of 
head,  neck,  and  chest,  also  right  arm. 

Pours  lymph  into  right  innominate 
vein. 

Superficial  —  beneath  skin,  accompany 
superficial  veins. 

Deep  —  accompany  deep  blood-vessels. 

Lymphatics  of  the  intestines. 

Many  originate  in  villi  of  small  in- 
testine. 

During  digestion  —  chyle. 


Contain 


During  period  of  fasting  — 


lymph. 

Absorb  fatty  substances. 
Expanded  lymph  spaces. 
Lymph  transudes  by  osmosis. 
Function  —  Drain  off  lymph  from  all  parts  of  the  body 
and  return  it  to  the  innominate  veins. 


Serous  Cavities 


196 


ANATOMY  AND  PHYSIOLOGY         [CHAP.  X 


Lymph  Nodes 


Description 


Location  . 


Function  . 


f  Round. 
Shape  <  r 

I  Ovoid. 

Size  varies  from  pinhead  to  almond. 

f Connective  and  mus- 
Outer  capsule  \          , 

I      cular  tissue. 

Interior  divided  into  irregular  spaces 
like  sponge. 

Spaces  partially  filled  with  reticular 
adenoid  tissue.  Communicating 
channels  for  lymph,  which  enters  by 
afferent,  leaves  by  efferent  vessels. 

Are  well  supplied  with  blood. 

Superficial  and  deep  set. 

Usually  arranged  around  blood- 
vessels. 

Neck,  thorax,  axilla,  groin,  mesentery. 

In  the  arms  as  far  as  elbows. 

In  the  legs  as  far  as  popliteal  space. 

Usually  name  indicates  location. 

1 .  Filters  —  preventive    and    protec- 

tive. 

2.  Multiplication  of  leucocytes. 


CHAPTER  XI 


THE  VASCULAR  SYSTEM  CONTINUED  :  ARTERIES  ;  PULMONARY 
SYSTEM;  GENERAL  SYSTEM;  VEINS;  SUPPLEMENTARY 
CHANNEL,  AND  PORTAL  SYSTEM 

ARTERIES 

THE  arteries,  which  carry  and  regulate  the  supply  of  blood  from 
the  heart  to  the  capillaries,  are  distributed  throughout  the  body 
in  a  systematic  manner,  and  before  attempting  the  study  of  the 

CAPILLARY   NETWORK 


TERMINAL  BRANCHES 
CALLED  ARTERIOLES 
END  IN    CAPILLARIES 


ANASTOMOSIS 


RECURRENT 
BRANCH 


FIG.  125. 


DIAGRAM  SHOWING  THE  BRANCHINGS,  ANASTOMOSES,  AND  CONFLU- 
ENCE OF  ARTERIES.     (Gerrish.) 


circulation,  we  must  try  to  gain  a  general  idea  of  this  system  of 
distribution,  in  order  that  we  may  be  able  to  locate  the  position 
of  these  important  vessels.  The  arteries  usually  occupy  protected 

197 


198  ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 

situations,  that  they  may  be  exposed  as  little  as  possible  to  acci- 
dental injury,  or  to  the  effects  of  local  pressure. 

Division.  —  As  they  proceed  in  their  course  they  divide  into 
branches,  the  division  taking  place  in  different  ways. 

(1)  An  artery  may  at  once  resolve  itself  into  two  branches  of 
nearly  equal  size  (dichotomous  division,  or  splitting  in  two). 

(2)  It  may  give  off  several  branches  in  succession  and  still  main- 
tain its  character  as  a  trunk. 

(3)  It  may  give  off  one  branch  that  divides  into  three  equal 
branches.     In  this  case  the  parent  branch  is  called  an  axis.     Ex- 
ample —  coeliac  axis. 

Anastomosis  or  inosculation.  —  The  distal  ends  of  arteries  unite 
at  frequent  intervals,  when  they  are  said  to  anastomose,  or  inoscu- 
late. Such  inosculations  admit  of  free  communication  between 
the  currents  of  the  blood,  tend  to  obviate  the  effects  of  local  in- 
terruption, and  to  promote  equality  of  distribution  and  of  pres- 
sure. This  arrangement  makes  it  possible  to  tie  veins  and  arteries 
during  operations,  or  after  injuries,  without  serious  interference 
with  the  circulation. 

Plexus.  —  A  plexus  or  network  is  formed  by  the  inosculations 
of  a  number  of  arteries  in  a  limited  area.  Arteries  usually 
pursue  a  tolerably  straight  course,  but  in  some  parts  of  the 
body  they  are  tortuous.  The  facial  artery,  in  its  course  over  the 
face,  and  the  arteries  of  the  lips  are  extremely  tortuous,  so  that 
they  may  accommodate  themselves  to  the  movements  of  the 
parts. 

Divisions  of  the  vascular  system.  —  The  blood-vessels  of  the 
body  are  arranged  in  two  main  systems,  namely,  the  pulmonary 
and  the  general  or  systemic. 

THE  PULMONARY  SYSTEM 

The  pulmonary  system  is  the  lesser  system  and  provides  for 
the  circulation  of  the  blood  from  the  right  ventricle  to  the 
lungs,  and  then  back  to  the  left  auricle.  This  is  called  the  pul- 
monary circulation. 

Blood-vessels  of  the  pulmonary  system.  —  The  blood-vessels 
of  the  pulmonary  system  are  (1)  the  pulmonary  artery  and  all  its 
branches,  (2)  the  capillaries  which  connect  these  branches  with 
the  veins,  and  (3)  the  pulmonary  veins. 


CHAP.  XI]          THE  PULMONARY  SYSTEM 


199 


The  pulmonary  artery.  —  The  pulmonary  artery  conveys  the 
venous  blood  from  the  right  side  of  the  heart  to  the  lungs.     The 


Facial 


Temporal 

External  carotid 
Common  carotid 
Suhclavian 
Aorta 


Axillary 


Brachial 


Radial 
Ulnar 

Palmar  arch. 


Femoral 
Popliteal 

Anterior  tibial 

Posterior  tibial 
Dorsalis  pedis 


FIG.  126.  —  THE  PRINCIPAL  ARTERIES  OF  THE  BODY.     (Morrow.) 

main  trunk  is  a  short,  wide  vessel  about  two  inches  (5  cm.)  in 
length  and  a  little  more  than  one  inch  (about  3  cm.)  in  diameter. 
It  arises  from  the  right  ventricle,  in  front  of  the  aorta,  and  runs 
for  a  distance  of  two  inches  (5  cm.)  upward,  backward,  and  to 


200 


ANATOMY  AND  PHYSIOLOGY        [CHAP.  XI 


the  left.  (See  Fig.  107.)  On  a  level  with  the  intervertebral  disc, 
between  the  fifth  and  sixth  thoracic  vertebrae,  it  divides  into  two 
branches,  the  right  and  left  pulmonary  arteries  which  pass  to  the 
right  and  left  lungs.  From  these  main  branches,  arteries  arise 
which  divide  and  subdivide,  grow  smaller  in  size,  and  finally  merge 


Branch  of  pul- 
....  monary  artery 
Entrance  of 
vena  azygos 


FIG.  127.  —  PULMONARY  VEINS,  SEEN  IN  A  DORSAL  VIEW  OF  THE  HEART  AND 
LUNGS.  The  left  lung  is  pulled  to  the  left,  and  the  right  lung  has  been  partly  cut 
away  to  show  the  ramifications  of  the  air-tubes  and  blood-vessels.  (Gerrish.) 


into  capillaries  which  form  a  network  upon  the  walls  of  the  air- 
cells.1  These  capillaries  unite,  grow  larger  in  size,  and  gradually 
assume  the  characteristics  of  veins.  The  veins  unite  to  form  the 
pulmonary  veins. 

The  pulmonary  veins.  — -  The  pulmonary  veins  are  four  short 
trunks  which  convey  the  blood  from  the  lungs  to  the  left  auricle, 
and  are  found,  two  on  each  side,  —  in  the  root  of  the  corresponding 
lung.  The  pulmonary  veins  have  no  valves. 

1  See  page  257. 


CHAP.  XI] 


THE  VASCULAR   SYSTEM 


201 


THE    GENERAL    SYSTEM 

The  general  system  is  the  larger  system  and  provides  for  the 
circulation  of  blood  from  the  left  ventricle  to  all  parts  of  the 
body    by   means    of  the 
aorta   and   its    branches, 
and    the    return    to  the 
right  auricle  by  means  of 
the  venae  cavse.     This  is 
called  the  systemic  circu- 
lation. 

The  blood-vessels  of 
the  general  system.  - 
The  blood-vessels  of  the 
general  system  consist  of 
(1)  the  aorta,  and  all  the 
arteries  that  originate 
from  it,  including  the 
terminal  branches  called 
arterioles ;  (2)  the  capil- 
laries which  connect  the 
arterioles  and  venules ; 
(3)  all  the  venules  and 
veins  of  the  body  which 
empty  either  directly  into 
the  heart,  or  indirectly  by 
means  of  the  superior  and 
inferior  venae  cavae. 

The  aorta.  —The  aorta 
is  the  main  trunk  of  the 
arterial  system.  Spring- 
ing from  the  left  ventricle 
of  the  heart,  it  arches 
over  the  root  of  the  left  lung,  descends  along  the  vertebral  column, 
and  after  passing  through  the  diaphragm  into  the  abdominal 
cavity,  ends  opposite  the  fourth  lumbar  vertebra  by  dividing  into 
the  right  and  left  common  iliac  arteries.  In  this  course  the  aorta 
forms  a  continuous  trunk,  which  gradually  diminishes  in  size  from 
its  commencement  to  its  termination  (from  one  and  one-eighth 


FIG.  128.  —  THORACIC  AORTA.     (Gerrish.) 


202 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 


inches  or  2.8  cm.  to  seven-tenths  of  an  inch  or  1.75  cm.).     It  gives 
off  large  and  small  branches  at  various  points. 


Adrenal  or 

Supra-renal 

gland 


A  lumbar  vein 


FIG.  129.  —  THE  ABDOMINAL  AORTA  AND  INFEKIOH  VENA  CAVA.     (Gerrish.) 

It  may  be  divided  as  follows  :  (1)  the  ascending  aorta  is  the  short 
part  which  is  contained  within  the  pericardium. 

(2)  The  arch  is  about  two  inches  (5  cm.)  in  length  and  extends 


CHAP.  XI]  THE   GENERAL   SYSTEM  203 

from  the  ascending  aorta  to  the  border  of  the  fourth  thoracic 
vertebra.  It  forms  a  well-marked  curve  in  front  of  the  trachea 
and  around  the  root  of  the  left  lung. 

(3)  The  descending  thoracic  aorta  is  the  comparatively  straight 
part  that  extends  from  the  lower  border  of  the  fourth  thoracic 
vertebra  on  the  left  side,  to  the  aortic  opening  in  the  diaphragm 
in  front  of  the  lower  border  of  the  last  thoracic  vertebra.     It  has 
a  length  of  from  seven  to  eight  inches  (17.5  to  20  cm.). 

(4)  The  abdominal  aorta  commences  at  the  aortic  opening  of 
the  diaphragm,  in  front  of  the  lower  border  of  the  last  thoracic 
vertebra,  and  terminates  below  by  dividing  into  the  two  common 
iliac  arteries.     The  bifurcation  usually  takes  place  about  halfway 
down  the  body  of  the  fourth  lumbar  vertebra,  which  corresponds 
to  a  spot  on  the  front  of  the  abdomen,  slightly  below  and  to  the 
left  of  the  umbilicus.     Its  length  is  about  five  inches  (12.5  cm.). 

Branches  of  the  ascending  aorta.  —  The  only  branches  of  the 
ascending  aorta  are  the  right  and  left  coronary  arteries.  They 
arise  immediately  above  the  semilunar  valves  and  encircle  the 
heart,  giving  off  numerous  branches  that  supply  the  heart  muscle. 
(See  Fig.  112.) 

Branches  of  the  arch  of  the  aorta.  —  The  branches  given  off  from 
the  arch  of  the  aorta  are  three  in  number  —  the  innominate,  the  left 
common  carotid,  and  the  left  subclavian  arteries.  (See  Fig.  107.) 

The  innominate  (brachio-cephalic)  artery  arises  from  the  right 
upper  surface  of  the  arch,  ascends  obliquely  toward  the  right, 
until,  arriving  on  a  level  with  the  upper  margin  of  the  clavicle, 
it  divides  into  the  right  common  carotid  and  right  subclavian 
arteries.  Its  usual  length  is  from  one  to  two  inches  (2.5  to 
5  cm.).  (See  Fig.  107.) 

The  left  common  carotid  arises  from  the  middle  of  the  upper 
surface  of  the  arch  of  the  aorta,  and  the  right  common  carotid 
arises  at  the  division  of  the  innominate,  consequently  the  left 
carotid  is  an  inch  or  two  longer  than  the  right.  They  ascend 
obliquely  on  either  side  of  the  neck  until,  on  a  level  with  the 
upper  border  of  the  laryngeal  prominence  (Adam's  apple),  they 
divide  into  two  great  branches :  (1)  the  external  carotid,  (2)  the 
internal  carotid.  At  the  root  of  the  neck  the  common  carotids 
are  separated  from  each  other  by  only  a  narrow  interval,  corre- 
sponding with  the  width  of  the  trachea;  but  as  they  ascend 


204  ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 

they  are  separated  by  a  much  larger  interval,  corresponding  with 
the  breadth  of  the  larynx  and  pharynx. 

Each  external  carotid  has  eight  branches,  which  are  distributed 
to  the  throat,  tongue,  face,  ears,  and  walls  of  the  cranium. 


FIG.  130.  —  SUBCLAVIAN  AND  AXILLARY  ARTERIES.     (Gerrish.) 

Each  internal  carotid  has  many  branches  which  are  distributed 
to  the  brain  and  eyes.  The  chief  ones  are  the  cerebral  and 
ophthalmic. 

Circle  of  Willis.  —  The  circle  of  Willis  is  a  remarkable  anastomo- 
sis formed  by  the  blood-vessels  of  the  brain.  It  is  situated  at  the 
base  of  the  brain  and  is  formed  by  the  union  of  (1)  the  anterior 
and  posterior  cerebral  arteries,  which  are  branches  of  the  internal 
carotid,  and  (2)  branches  of  the  basilar  artery,  which  is  formed  by 
the  union  of  the  two  vertebrals.1  These  arteries  are  joined  in  such 

1  The  vertebral  arteries  are  branches  given  off  from  the  subclavian.  They  ascend 
on  either  side  of  the  vertebral  column,  pass  through  the  foramen  magnum,  and  at 
the  base  of  the  brain  unite  to  form  the  basilar  artery. 


CHAP.  XI] 


THE   GENERAL   SYSTEM 


205 


a  manner  as  to  form  a '  complete  circle,  and  this  arrangement 
(1)  equalizes  the  circulation  of  the  blood  in  the  brain,  and  (2)  in 
case  of  destruction  of  one  of  the  arteries,  provides  for  the  blood 
reaching  the  brain  through  .other  vessels. 

The  subclavian  arteries.  —  The  right  subclavian  arises  at  the 
division  of  the  innominate,  and  the  left  subclavian  from  the  arch 
of  the  aorta.  The  subclavian  arteries  are  the  first  portions  of  a 
long  trunk  which  forms  the  main  artery  of  the  upper  limb,  and 


ANTERIOR  CEREBRAL 


INTERNAL  CAROTID 


POSTERIOR  CEREBRAL 
BASILAR 


VERTEBRAL 


FIG.  131.  —  DIAGRAM  OF  THE  CIRCLE  OF  WILLIS. 

which  is  artificially  divided  for  purposes  of  description  into  three 
parts;  viz.:  (1)  Subclavian,  (2)  Axillary,  and  (3)  Brachial. 

The  subclavian  artery  passes  a  short  way  up  the  thorax  into  the 
neck,  and  then  turns  downward  to  rest  on  the  first  rib.  At  the 
lower  border  of  the  first  rib  it  ceases  to  be  called  subclavian,  and 
is  continued  as  the  axillary.  It  gives  off  large  branches  to  the 
brain,  back,  chest,  and  neck. 

The  axillary  artery  passes  through  the  axilla,  lying  to  the  inner 
side  of  the  shoulder  joint  and  upper  part  of  the  arm.  It  gives  off 
branches  to  the  chest,  shoulder,  and  arm. 

The  brachial  artery  (continuation  of  the  axillary)  extends  from 
the  axillary  space  to  just  below  the  bend  of  the  elbow,  where  it 
divides  into  the  ulnar  and  radial  arteries.  It  may  be  readily  lo- 


206 


ANATOMY  AND  PHYSIOLOGY        [CHAP.  XI 


Radial 


cated,  lying  in  the  depression  along  the  inner  border  of  the  biceps 
muscle.     Pressure  made  at  this  point  from  within  outward  against 

the  humerus  will  control  the  blood 
supply  to  the  arm. 

The  ulnar,  the  larger  of  the  two 
vessels  into  which  the  brachial  divides, 
extends  along  the  inner  side  of  the 
forearm  into  the  palm  of  the  hand, 
where  it  terminates  in  the  superficial 
palmar  arch. 

The  radial  artery  appears,  by  its 
direction,  to  be  a  continuation  of  the 
brachial,  although  it  does  not  equal 
the  ulnar  in  size.  It  extends  along 
the  outer  side  of  the  front  of  the  fore- 
arm as  far  as  the  lower  end  of  the 
radius,  below  which  it  turns  around 
the  outer  border  of  the  wrist,  and 
passes  forward  into  the  palm  of  the 
hand.  It  terminates  in  the  deep 
palmar  arch.  The  superficial  and 
deep  palmar  arches  anastomose  and 
supply  the  hand  with  blood. 

Branches  of  the  thoracic  aorta.  - 
The  branches  derived  from  the  tho- 
racic aorta  are  numerous  but  small, 
and  the  consequent  decrease  in  size  is 
not  marked.  The  principal  branches 
are  (1)  the  bronchial,  (2)  the  cesopha- 
geal,  (3)  the  mediastinal,  (4)  the  peri- 
cardial,  and  (5)  the  intercostal. 

(1)  The  bronchial  arteries  are  the 
nutrient  vessels  of  the  lungs,  and 
vary  in  number,  size,  and  origin.  As 
a  rule,  there  are  two  left  bronchial 
arteries  and  one  right.  The  left  arise 
from  the  thoracic  aorta,  and  the  right  arises  from  the  first  aortic 
intercostal  or  from  the  left  bronchial.  Each  vessel  runs  along  the 
back  part  of  the  corresponding  bronchus,  dividing  and  subdivid- 


FIG.  132.  —  DEEP  ANTERIOR 
VIEW  OF  THE  ARTERIES  OF  THE 
ARM,  FOREARM,  AND  HAND. 


CHAP.  XI]  THE   GENERAL   SYSTEM  207 

ing  along  the  bronchial  tubes,  supplying  them,  and  the  cellular 
tissue  of  the  lungs. 

(2)  The  oesophageal  arteries  are  four  or  five  in  number  and 
form  a  chain  of  anastomoses  along  the  oesophagus.     They  anasto- 
mose with  branches  of  the  thyroid  arteries  above,  and  with  ascend- 
ing branches  from  the  gastric  and  phrenic  arteries  below. 

(3)  The  mediastinal  arteries  are  numerous  small  arteries  which 
supply  the  nodes  and  areolar  tissue  in  the  posterior  mediastinum. 
(See  page  257.) 

(4)  The  pericardial  arteries  are  small  and  are  distributed  to 
the  pericardium. 

(5)  The  intercostal  arteries  are  ten  or  eleven  on  each  side.    They 
are  subdivided  into  the  superior  and  aortic  intercostals.     The  su- 
perior intercostal  artery  which  is  a  branch  of  the  subclavian  sup- 
plies the  two  superior  intercostal  spaces  on  each  side.     The  aortic 
intercostals  are  usually  nine  in  number  on  each  side  and  arise  from 
the  back  of  the  aorta.     Each  intercostal  artery  is  accompanied  by 
a  vein  and  nerve ;  and  each  one  gives  off  numerous  branches  to  the 
muscles  and  skin.     (See  Fig.  128.) 

Branches  of  the  abdominal  aorta.  —  Branches  of  the  abdominal 
aorta  may  be  divided  into  two  sets :  — 

1.  Visceral,  or  those  which  supply  the  viscera. 

2.  Parietal,  or  those  which  are  distributed  to  the  walls  of  the 
abdomen. 

Visceral  group.  —  The  visceral  group  includes  (a)  the  coeliac 
axis;  (b)  the  right  and  left  supra-renal;  (c)  the  superior 
mesenteric ;  (d)  the  right  and  left  renal ;  (e)  the  right  and  left  sper- 
matic or  right  and  left  ovarian ;  and  (/)  the  inferior  mesenteric. 

(a)  The  coeliac  axis  is  a  short,  wide  vessel,  usually  not  more  than 
half  an  inch  (1.25  cm.)  in  length,  which  arises  from  the  front  of  the 
aorta,  just  below  the  opening  in  the  diaphragm.  It  divides  into 
three  branches ;  viz.  (1)  the  gastric,  which  supplies  the  stomach ; 
(2)  the  hepatic,  which  supplies  the  liver  and  the  duodenum,  or 
portion  of  the  intestine  nearest  to  the  stomach ;  and  (3)  the 
splenic,  which  supplies  the  spleen,  and  also  takes  part  in  the  blood 
supply  of  the  stomach  and  pancreas.  (See  Fig.  129.) 

(6)  The  supra-renal  arteries  are  of  small  size.     They  arise  from 
the  side  of  the  aorta  and  supply  the  supra-renal  or  adrenal  bodies. 
(See  page  345  and  Fig.  129.) 


208  ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 

(c)  The  superior  mesenteric  artery  arises  from  the  fore  part  of 
the  aorta,  a  little  below  the  supra-renals.  It  supplies  the  small 
intestine  beyond  the  first  portion,  and  half  of  the  large  intestine. 
(See  Fig.  129.) 


FIG.   133.  —  SUPERIOR  MESENTERIC  ARTERY.     (Gerrish.) 

(d)  The  renal  arteries  are  of  large  size,  in  proportion  to  the  bulk 
of  the  organs  (kidneys)  which  they  supply.     They  arise  from  the 
sides  of  the  aorta,  below  the  superior  mesenteric  artery,  that  of 
the  right  side  being  generally  a  little  lower  down  than  that  of  the 
left.     Each  is  directed  outward,  so  as  to  form  nearly  a  right  angle 
with  the  aorta.     (See  Fig.  129.) 

(e)  The  spermatic  arteries  in  the  male  arise  close  together  from 


CHAP.  XI] 


THE   GENERAL   SYSTEM 


209 
They 


the  front  of  the  aorta,  a  little  below  the  renal  arteries. 
are  distributed  to  the  testes. 

(/)  The  ovarian  arteries  in  the  female  arise  from  the  same  por- 
tion of  the  aorta  as  the  spermatic  arteries  in  the  male.  They 
supply  the  ovaries,  and,  joined  to  the  uterine  artery,  —  a  branch 


EScNTER   O 


INFERIOR 
HEMORRHOIDAL 


FIG.  134.  —  INFERIOR  MESENTERIC  ARTERY.     (Gerrish.) 

of  the  internal  iliac,  —  also  assist  in  supplying  the  uterus. 
During  pregnancy  the  ovarian  arteries  become  considerably 
enlarged. 

(g)  The  inferior  mesenteric  artery  arises  from  the  front  of  the 
aorta,  about  an  inch  and  a  half  (3.8  cm.)  above  its  bifurcation, 
and  supplies  the  lower  half  of  the  large  intestine.  Continued 


210  ANATOMY  AND  PHYSIOLOGY        [CHAP.  XI 

under  the  name  of  the  superior  hemorrhoidal  artery,  it  also  takes 
part  in  the  blood  supply  of  the  rectum.     (See  Fig.  129.) 

Parietal  group.  —  The  parietal  group  includes  (a)  the  right 
and  left  phrenic  arteries;  (6)  the  first,  second,  third,  and  fourth 
pairs  of  lumbar  arteries ;  and  (c)  the  middle  sacral. 

(a)  The  phrenic  arteries  arise  from  the  aorta  above  the  coeliac 
axis  and  are  distributed  to  the  diaphragm.     (See  Fig.  129.) 

(b)  The  lumbar  arteries  supply  the  muscles  and  walls  of  the 
respective  regions  that  their  names  suggest. 

(c)  The  middle  sacral  artery  arises  from  the  lower  end  of  the 
abdominal  aorta  and  passes  down  to  the  sacrum  and  coccyx. 

Common  iliac.  —  The  common  iliac  arteries,  commencing  at  the 
bifurcation  of  the  aorta,  pass  downward  and  outward  about  two 
inches  (5  cm.),  and  then  each  divides  into  the  internal  (or  hypo- 
gastric)  and  the  external  iliac  arteries. 

The  internal  iliac  artery  (or  hypogastric)  supplies  branches 
to  the  pelvic  walls,  pelvic  viscera,  the  external  genitals,  and  the 
buttocks.  The  uterine  artery  in  the  female,  which  supplies  the 
tissues  of  the  uterus  with  blood,  is  a  very  important  branch  .of  the 
internal  iliac. 

The  external  iliac  is  placed  within  the  abdomen,  and  extends 
from  the  bifurcation  of  the  common  iliac  to  the  lower  border  of 
the  inguinal  ligament. 

It  forms  a  large,  continuous  trunk,  which  extends  downward 
in  the  lower  limb,  and  is  named  in  successive  parts  of  its  course, 
femoral,  popliteal,  and  posterior  tibial. 

The  femoral  artery  lies  in  the  upper  three-fourths  of  the  thigh, 
its  limits  being  marked  above  by  the  inguinal  (Poupart's)  liga- 
ment and  below  by  the  opening  in  the  great  adductor  muscle. 
After  passing  through  this  opening  the  artery  receives  the  name 
of  popliteal.  In  the  first  part  of  its  course  the  artery  lies  along  the 
middle  of  the  depression  on  the  inner  aspect  of  the  thigh,  known 
as  Scarpa's  triangle.1  In  this  situation  the  beating  of  the  artery 
may  be  felt,  and  the  circulation  through  the  vessel  may  be  most 
easily  controlled  by  pressure. 

1  Scarpa's  triangle  is  a  name  given  to  a  triangular  space  situated  on  the  upper, 
anterior,  and  inner  surface  of  the  thigh.  It  is  bounded  above  by  Poupart's  liga- 
ment, on  the  outer  side  by  the  sartorius  muscle,  and  on  the  inner  side  by  the  ad- 
ductor. 


CHAP.  XI] 


THE   GENERAL   SYSTEM 


211 


The  popliteal  artery,  continuous  with  the  femoral,  is  placed  at 
the  back  of  the  knee ;  just  below  the  knee-joint  it  divides  into  the 
posterior  tibial  and  anterior  tibial  arteries. 

The  posterior  tibial  artery  lies  along  the  back  of  the  leg,  and 
extends  from  the  bifurcation  of  the  popliteal  to  the  ankle,  where 
it  divides  into  the  internal  and  external  plantar  arteries. 


ANTERIOR    CRURA 
NERVE 


EXTERNAL 
C/RCUMFLEX 


SUPERFICIAL    EPIGASTRIO 


SUPERFICIAL    EXTERNAL 
PUDIC 


EEP    EXTERNAL 
PUDIC 


SUPERIOR    EXTERNA 
ARTICULAR 


INFERIOR    EXTERNA 
ARTICULAR 


ANASTOMOTICA 
MAGNA 


INFERIOR    INTERNAl 
ARTICULAR 


FIG.   135.  —  FEMORAL,  ARTERY.     (Gerrish.) 


212 


ANATOMY  AND  PHYSIOLOGY       [CHAP.  XI 


ANTERIOR   TIBIAL 
RECURRENT — i 


ANTERIOR    TIBIAL 
NERVE 


ANTERIOR 
PERONEAL 


EXTERNAL 

MALi-EOLAR 


INTERNAL 
MALLEOLAR 


FIG.  136.  —  ARTERIES  uv  THE  DORSAL 
PART  OF  THE  LEG.     (Gerrish.) 


FIG.  137.  —  ANTERIOR  TIBIAL  ARTERY. 
(Gerrish.) 


CHAP.  XI] 


VEINS 


213 


The  peroneal  artery  is  a  large  branch  given  off  by  the  posterior 
tibial  just  about  an  inch  (25  mm.)  below  the  bifurcation  of  the 
popliteal. 

The  anterior  tibial  artery,  the  smaller  of  the  two  divisions  of 
the  popliteal  trunk,  extends  along  the  front  of  the  leg  to  the  bend 
of  the  ankle,  whence  it  is 
prolonged  into  the  foot 
under  the  name  of  the  dor- 
salis  pedis  artery.  This 
unites  with  the  external 
and  internal  plantar  ar- 
teries to  form  the  plantar 
arch  which  supplies  blood 
to  the  foot.1 

VEINS 

The  arteries  begin  as 
large  trunks,  which  gradu- 
ally become  smaller  and 
smaller  until  they  end  in 
arterioles,  which  merge  into 
capillaries,  while  the  veins 
begin  as  small  branches 
called  venules  which  at  first 
are  scarcely  distinguishable 
from  the  capillaries,  and 
unite  to  form  larger  and 
larger  vessels.  They  differ 
from  the  arteries  in  their 
larger  capacity,  greater 
number,  thinner  walls,  and 

in  the  presence  of  valves  which  prevent  backward  circulation. 
The  veins  may  be  divided  into  two  sets  —  a  superficial  and  a  deep 
set. 

The  superficial  set  —  are  found  immediately  beneath  the  skin. 

The  deep  set  —  accompany  the  arteries  and  are  usually  called 
by  the  same  names. 


FIG.  138.  —  ARTERIES  OF  THE  DORSUM  OF 
THE  FOOT.  Of  the  dorsal  interosseous  only 
the  second  is  labelled.  (Gerrish.) 


1  Drawing  the  outline  of  the  aorta  with  its  branches  as  an  arterial  tree  will 
greatly  aid  the  student  in  mastering  the  arterial  distribution. 


214  ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 

Sometimes  two  deep  veins  accompany  an  artery,  and  are  then 
called  venae  comites,  or  companion  veins,  or  one  vein  may 
accompany  an  artery,  and  then  be  known  as  the  vena  comes  of 
that  artery.  The  superficial  and  the  deep  veins  have  very  frequent 
communications  with  each  other,  and  the  anastomoses  of  veins 
are  always  more  numerous  than  those  of  arteries. 

The  systemic  veins.  —  The  systemic  veins  are  naturally  divided 
into  two  groups :  - 

1.  Those  from  which  the  blood  is  carried  to  the  heart  by  the 
superior  vena  cava,  viz.  the  veins  of  the  head,  neck,  upper  extremi- 
ties, and  the  walls  of  the  thorax.     In  this  group  we  include  the 
veins  of  the  heart,  which,  however,  pass  directly  into  the  right 
auricle  without  entering  the  superior  vena  cava. 

2.  Those  from  which  the  blood  is  carried  to  the  heart  by  the 
inferior  vena  cava,  viz.  the  veins  of  the  lower  limbs,  the  lower 
part  of  the  trunk,  and  the  abdominal  viscera. 

(1)    Superior  vena  cava  group. 

Veins  of  the  head  and  neck.  —  The  blood  returning  from  the 
head  and  neck  flows  on  each  side  into  two  principal  veins,  the 
external  and  internal  jugular. 

External  jugular  veins.  —  The  right  and  left  external  jugular 
veins  are  formed  in  the  substance  of  the  parotid  glands  by  the 
union  of  two  of  the  veins  of  the  face.  This  union  takes  place  on  a 
level  with  the  angle  of  the  lower  jaw,  and  each  vein  descends  al- 
most vertically  in  the  neck  to  its  termination  in  the  subclavian. 
These  two  veins  receive  the  blood  from  the  face  and  the  exterior 
of  the  cranium. 

Internal  jugular  veins.  —  These  veins  begin  at  the  base  of  the 
skull  and  descend  on  either  side  of  the  neck,  first  with  the  external 
carotid,  then  with  the  common  carotid,  and  join  at  a  right  angle 
with  the  subclavian  to  form  the  innominate  (brachio-cephalic) 
vein.  They  receive  the  blood  from  the  veins  and  sinuses  of  the 
cranial  cavity.  (See  Fig.  141.) 

Sinuses.  —  The  blood  from  the  interior  of  the  skull  is  returned 
to  the  large  veins  by  venous  channels  that  are  called  sinuses. 
They  are  formed  by  a  separation  of  the  layers  of  the  dura  mater, 
the  fibrous  membrane  which  covers  the  brain.  Their  outer  wall 
consists  of  the  dura  mater,  and  their  inner  lining  of  endothelium 


CHAP.  XI] 


VEINS 


215 


is  continuous  with  the  lining  membrane  of  the  vessels  that  com- 
municate with  them.     (See  Fig.  202.) 

Veins  of  the  upper  extremities.  —  The  blood  from  the  upper 
limbs  is  returned  by  a  deep  and  a  superficial  set  of  veins.  The 
deep  veins  are  the  venae  comites  of  the  forearm  and  arm  and  are 


CEPHALIC — 


MEDIAN 
CEPHALIC' 


RADIAL 


MEDIAN 


•-BASILIC 


MEDIAN  BASILIC 

COMMON  ULNAR 

BRANCH   FROM 

DEEP  SET 

POSTERIOR  ULNAR 


FIG.  139.  —  SUPERFICIAL  VEINS  OF  FRONT  OF  FOREARM  AND  LOWER  PART  OF 

ARM.     (Gerrish.) 

called  by  the  same  names  as  the  arteries.  They  communicate 
with  the  superficial  veins  at  the  hand  and  elbow,  and  the  vena 
comes  of  the  brachial  artery  unites  with  a  superficial  vein,  i.e.,  the 
basilic,  to  form  the  axillary  vein. 

The  superficial  veins.  —  The  superficial  veins  are  much  larger 
than  the  deep,  and  take  a  greater  share  in  returning  the  blood, 


216  ANATOMY  AND  PHYSIOLOGY        [CHAP.  XI 

especially  from  the  distal  portion  of  the  limb.     They  commence 
in  two  plexuses,  one  on  the  back  of  the  hand  and  one  on  the  front 
.  of  the  wrist.     They  comprise  the  following :  — 

(1)  The  radial  vein  begins  in  the  dorsal  plexus  and  runs  up 
the   radial   side   of  the   forearm  to   a  little  above  the  bend  of 
the  elbow,  where  it  joins  the  median  cephalic  vein  to  form  the 
cephalic.  * 

(2)  The  posterior  ulnar  begins  in  the  dorsal  plexus  and  extends 
upward  along  the  back  part  of  the  ulnar  side  of  the  forearm. 
Near  the  bend  of  the  elbow  it  usually  receives  the  anterior  ulnar 
vein. 

(3)  The  anterior  ulnar  vein  ascends  from  the  wrist  along  the 
ulnar  side  of  the  front  of  the  forearm. 

(4)  The  common  ulnar  is  formed  by  the  union  of  the  anterior 
and  posterior  ulnar  veins  just  below  the  elbow,  and  after  a  short 
course  it  joins  the  median  basilic. 

(5)  The  median  vein  begins  in  the  plexus  on  the  wrist  and 
ascends  along  the  front  of  the  forearm  to  the  bend  of  the  elbow 
where  it  bifurcates  into  the  median  basilic  and  median  cephalic 
veins. 

(6)  The  median  basilic  is  directed  upward  and  joins  the  com- 
mon ulnar  to  form  the  basilic  vein.     The  median  basilic  is  the  vein 
usually  chosen  for  the  operation  of  phlebotomy  or  intravenous  in- 
fusion. 

(7)  The  median  cephalic  vein  is  directed  upward  and  joins  the 
radial  vein  to  form  the  cephalic. 

(8)  The  basilic  vein  ascends  in  the  groove  on  the  inner  side  of 
the  biceps.     It  unites  with  the  inner  vena  comes  of  the  brachial 
artery  to  form  the  axillary  vein. 

(9)  The  cephalic  vein  ascends  in  the  groove  external  to  the 
biceps  and  ends  in  the  axillary  vein. 

The  axillary  vein.  —  The  axillary  vein  begins  at  the  junction  of 
the  inner  brachial  and  the  basilic,  and  ends  at  the  outer  border 
of  the  first  rib,  in  the  subclavian.  This  vein  accompanies 
the  axillary  artery  and  collects  all  the  blood  of  the  upper  ex- 
tremities. 

The  subclavian  vein.  —  This  vein  continues  the  axillary  from 
the  first  rib  to  the  joint  between  the  sternum  and  clavicle,  where  it 
unites  with  the  internal  jugular  to  form  the  innominate  vein. 


CHAP.  XI] 


VEINS 


217 


The  innominate  veins.  —  The  innominate  (brachio-cephalic) 
veins,  commencing  on  each  side  by  the  union  of  the  subclavian 
and  internal  jugular,  transmit  the  blood  returning  from  the  head 
and  neck,  the  upper  limbs,  and  a  part  of  the  thoracic  wall ;  they 
end  below  by  uniting  to  form  the  superior  vena  cava.  Both  in- 
nominate veins  are  joined  by  many  side  tributaries ;  they  also 


CEPHALIC  VEIN) 

ENTERING          f 
AXILLARY  ) 


SUBCLAVIAN 
VEIN 


AXILLARY 


(BASILIC  VEIN 
"\  PERFORATING 
(DEEP  FASCIA 


..-B  AS  I  Lid   VEIN 


FIG.  140.  —  SUPERFICIAL  VEINS  OF  FRONT  OF  ARM  AND  SHOULDER.     (Gerrish.) 

receive,  at  the  junction  of  the  subclavian  and  internal  jugular,  the 
lymph ;  on  the  left  side  from  the  thoracic  duct,  and  on  the  right 
from  the  right  lymphatic  duct. 

The  superior  vena  cava.  —  The  superior,  or  descending,  vena 
cava,  is  formed  by  the  union  of  the  right  and  left  innominate 
veins,  just  behind  the  junction  of  the  first  right  costal  cartilage 
with  the  sternum.  It  is  about  three  inches  (7.5  cm.)  long,  and 
opens  into  the  right  auricle,  opposite  the  third  rib. 

Thoracic  veins.  —  The  great  majority  of  the  thoracic  veins 
follow  the  same  course  as  the  arteries,  and  bear  the  same  names. 


218  ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 

Two  exceptions  are  the  inferior  vena  cava  and  the  azygos  veins 
which  wyill  be  described  later. 


FACIAL 


INTERNAL 
MAMMARY 


FIG.   141.  —  VEINS  OF  THE  NECK  AND  UPPER  PART  OF  THORAX.     Front  View. 

(Gerrish.) 

(2)    The  inferior  vena  cava  group. 

Veins  of  the  lower  extremities.  —  The  blood  from  the  lower 
limbs  is  also  returned  by  a  deep  and  a  superficial  set  of  veins. 
They  are  more  abundantly  supplied  with  valves  than  the  veins  of 
the  upper  limbs. 

The  deep  veins.  —  Below  the  knee  the  deep  veins  accompany 
the  arteries  in  pairs,  as  vense  comites,  and  as  in  the  upper  limbs  are 
called  by  the  same  names.  The  veins  from  the  foot  empty  into 
anterior  tibial  and  posterior  tibial  veins.  They  unite  to  form  the 


CHAP.  XI] 


VEINS 


219 


single  popliteal  vein,  which  is  continued  as  the  femoral  and  becomes 
the  external  iliac. 

The  superficial  veins.  —  The  internal  or  long  saphenous  and  the 
external  or  short  saphenous  are  the  two  largest  superficial  veins. 


I 


FIG.  142.  —  SUPERFICIAL 
VEINS  OF  THE  FRONT  OF  THE 
LEG  AND  FOOT.  (Gerrish.) 


FIG.  143.  —  SUPERFICIAL  VEINS 
OF  THE  FRONT  OF  THE  RIGHT 
THIGH.  (Gerrish.) 


220 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 


The  internal  saphenous  extends  from  the  ankle  to  within  an 
inch  and  a  half  (3.8  cm.)  of  the  inguinal  ligament.  It  lies  along 
the  inner  side  of  the  leg  and  thigh  and  ter- 
minates in  the  femoral  vein. 

The  external  saphenous  arises  from  the 
sole  of  the  foot,  and,  passing  up  the  back  of 
the  leg,  ends  in  the  deep  popliteal. 

The  femoral  veins.  —  These  vessels  are 
a  continuation  of  the  popliteal  veins  and 
extend  from  the  opening  in  the  adductor 
magnus  to  the  level  of  the  inguinal  liga- 
ment. 

The  external  iliacs.  —  These  vessels  are  a 
continuation  of  the  femoral  veins,  and  extend 
from  the  level  of  the  inguinal  (Poupart's) 
ligament,  on  either  side,  to  the  joint  between 
the  sacrum  and  the  ilium.  They  receive 
the  blood  from  the  deep  and  superficial  veins 
of  the  lower  limbs.  (See  Fig.  129.) 

The  internal  iliacs. — They  are  formed  by 
the  union  of  veins  corresponding  to  the 
branches  of  the  internal  iliac  arteries.  They 
accompany  the  internal  iliac  arteries  and 
unite  with  the  external  iliac  veins  to  form 
the  common  iliacs.  (See  Fig.  129.) 

The  common  iliacs.  — The  common  iliacs 
extend  from  the  base  of  the  sacrum  to  the 
fourth  lumbar  vertebra,  and  then  the  two 
common  iliacs  unite  to  form  the  inferior  vena 
cava.  (See  Fig.  129.) 

The  inferior  vena  cava.  —  The  inferior,  or 
ascending,  vena  cava,  returns  the  blood 
from  the  lower  limbs,  pelvis,  and  abdomen. 

It  begins  at  the  junction  of  the  two  com- 
mon iliacs,  and  thence  ascends  along  the 
right  side  of  the  aorta,  perforates  the  diaphragm,  and  terminates 
by  entering  the  right  auricle  of  the  heart.  The  inferior  vena  cava 
receives  many  tributaries,  the  chief  of  which  are  the  lumbar, 
ovarian,  renal,  and  hepatic  veins.  (See  Fig.  129.) 


FIG.     144.  —  SUPER- 
FICIAL,  VEINS    OF    THE 

DORSUM     OF     THE     LEG. 

(Gerrish.) 


CHAP.  XI] 


VEINS 


221 


Supplementary  channel.  —  A  supplementary  channel  between 
the  inferior  and  superior  vena  cava  is  formed  by  the  azygos  veins. 
They  are  three  in  number  and  lie  on  the  sides  of  the  front  of  the 
vertebral  bodies. 


INTERNAL  JUGULAR 


SUBCLAVIAN 
RIGHT-^ 

INNOMINATE 


INTERNAL  JUGULAR 

EXTERNAL  JUGULAR 


UPPER    END  OF 
THORACIC    DUCT 


SUBCLAVIAN 

LEFT 

INNOMINATE 


ASCENDING   LUMBAR 


FIG.  145.  —  AZYGOS  AND  INTERCOSTAL  VEINS.  (Gerrish.) 

The  right  or  major  azygos  vein  is  an  upward  continuation  of  the 
lumbar  vein  which  communicates  with  the  common  iliac  vein, 
and  often  with  the  inferior  vena  cava  and  renal  vein.  It  ascends 


222 


ANATOMY  AND  PHYSIOLOGY        [CHAP.  XI 


FIG.  146.  —  PORTAL  SYSTEM  OF  VEINS.  The  liver  is  turned  upward  and  back- 
ward, and  the  transverse  colon  and  most  of  the  small  intestines  are  removed. 
(Gerrish.) 


CHAP.  XI]  THE  PORTAL  SYSTEM  223 

on  the  right  side  of  the  vertebral  column  to  the  level  of  the  fourth 
thoracic  vertebra,  where  it  empties  into  the  superior  vena  cava. 

The  left  lower  azygos  (minor)  vein  commences  on  the  left  side 
of  the  abdomen  in  a  manner  similar  to  the  right.  It  ascends  on 
the  left  side  of  the  vertebral  column,  and  at  about  the  level  of  the 
eighth  thoracic  vertebra  it  connects  with  the  right  azygos  vein. 

The  left  upper  azygos  vein  connects  above  with  the  superior 
intercostal  vein,  and  opens  below  into  either  the  left  lower  azygos, 
or  the  major  azygos  vein.  These  veins  receive  many  tributaries 
from  the  thoracic  walls  and  so  are  often  grouped  with  the  thoracic 
veins. 

It  is  important  to  remember  that  in  case  of  obstruction  in  the 
inferior  vena  cava  these  veins  form  a  supplementary  channel 
by  which  blood  can  be  conveyed  from  the  lower  part  of  the 
body  to  the  heart. 

The  portal  system.  —  The  gastric,  splenic,  inferior,  and  superior 
mesenteric  veins  which  bring  back  the  blood  from  the  intestinal 
tract  do  not  take  it  directly  to  the  inferior  vena  cava.  Just  back 
of  the  pancreas,  the  splenic  and  superior  mesenteric  unite  to  form 
the  portal  vein,  and  the  gastric  and  inferior  mesenteric  empty  into 
it.  The  portal  vein  runs  upward  and  to  the  right  for  about  three 
inches  (7.5  cm.),  then  enters  the  liver,  where  it  divides  into  many 
small  veins,  and  these  finally  form  plexuses  of  capillaries.  These 
capillaries  unite  with  another  set  of  capillaries  which  arise  from  the 
hepatic  artery,  and  form  the  hepatic  vein,  which  carries  the  blood 
from  the  liver  to  the  inferior  vena  cava.  Thus  it  will  be  seen  that 
the  liver  receives  blood  from  two  sources  —  (1)  the  portal  vein 
which  carries  blood  to  the  liver  in  order  that  certain  chemical 
changes  may  take  place,  and  (2)  the  hepatic  artery  which  carries 
blood  to  the  liver  for  nutritive  purposes.  The  blood  from  both 
sources  of  supply  is  carried  from  the  liver  by  the  hepatic  vein. 

The  portal  vein  and  all  its  branches  constitute  the  portal  system, 
which  is  often  described  as  a  third  or  accessory  system. 


224 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 


Arteries    , 


SUMMARY 

Begin  as  large  trunks,  grow  smaller. 
Usually  deep  seated  for  protection. 

Two  branches  of  nearly  equal  size. 
Division         Trunk  gives  off  several  branches. 

One  branch  that  serves  as  an  axis. 
Anastomosis  or  inosculation  —  distal  ends  unite. 
Plexus  —  many  inosculations  within  limited  area. 
Usually  straight  (facial  and  uterine  are  tortuous). 

Provides'  for  pulmonary  circulation. 

Right    pulmonary 


Pulmonary 

Divisions 

System 

of  the 

Vascular  ] 

System 

General 

System 

1.  Pulmonary  artery 


artery 

—  right  lung. 
Left  pulmonary  artery  — 
left  lung. 

2.  Capillaries  connect  arterioles  and  venules. 

3.  Four  pulmonary  veins  —  two  from  each  lung. 
Provides  for  systemic  circulation. 

1.  Aorta  and  all  its  branches. 

2.  Capillaries  connect  arterioles  and  venules. 

3.  Veins  empty  into  heart  either  directly  or  by 

means  of  inferior  and  superior  vena  cava. 


Aorta 


Ascending 
Aorta 

Right  and  left  coronary  —  supply  the  heart. 

Int.      carotid  —  brain 

Right    com- 

and eye. 

mon  caro- 

Ext.  carotid  —  throat, 

tid 

tongue,     face,     ears, 

Innominate 

12.  _      O      "„ 

walls  of  cranium. 
Superficial 

I. 
Arrh  of 

to  2  in. 

Right    sub- 

Ulnar         palmar 

f\l  \*1±    V/l  • 

clavian, 

arch. 

Aorta 

—  axil- 

2 in. 

lary  - 
brachial 

.  J  Deep    palmar 
Radial  i           , 
I      arch. 

Left   common   carotid  —  same   branches   as   right 

common  carotid. 

Left    subclavian  —  same   branches    as    right    sub- 

clavian. 

Bronchial  —  to  the  lung  tissue. 

II. 

(Esophageal  —  to  the  oesophagus. 

Thoracic 

Mediastinal  —  to  the  nodes  and  areolar  tissue  in 

Aorta 

the  mediastinum. 

7  to  8  in. 

Pericardial  —  to  the  pericardium. 

[  Intercostal  —  to  the  intercostal  spaces. 

CHAP.  XI] 


SUMMARY 


225 


f  Diaphragm  muscle  is  dividing  line  between  thoracic  and  ab- 
dominal aorta. 

Gastric  —  stomach, 
and 


Aorta 


III. 

Abdominal 
Aorta 
Sin. 


Visceral 
Group 


Parietal 
Group 


Cceliac    axis 


Sup. 
mesenteric 


Common 

Iliac 
Arteries 

2  in. 


Hepatic  —  liver 

duodenum. 
Splenic  spleen, 

stomach,  and  pan- 
creas. 
Supra-renal  —  supra-renal  bodies. 

Small    intestine,    ex- 
cept duodenum. 
Half   of   large   intes- 
tine. 

Renal  —  kidneys. 
Spermatic  —  testes. 
Ovarian  —  ovaries  and  uterus. 

Inf.  I  Lower   half   of   large 

mesenteric  intestine    and    rec- 

l      turn. 

Phrenic  —  diaphragm. 
Lumbar  —  dorsal,    spinal,    and    ab- 
dominal walls. 

Middle  sacral  —  sacrum  and  coccyx. 
Internal  iliac  —  walls  and  viscera  of  pelvis. 


Veins 


External 
iliac  — 
femoral 
popliteal 


Differ  from 
arteries 


Sets 


Posterior 
tibial 


Ext.  plantar  1  Plantar 
Int.  plantar  j      arch.  . 
Peroneal. 
Anterior      1 

tibial        I  Dorsalls  pedis' 

Begin  small,  grow  larger. 

Larger  capacity. 

Greater  number. 

Thinner  walls. 

Valves. 

More  frequent  anastomosis. 

Superficial. 

f  Venae  comites  —  companion  veins. 
Deep  . 

(  Vena  comes  —  companion  vein. 

Receive    blood  from  the  face  and  the  exterior  of 

the  cranium. 
Formed  in  parotid  gland,  terminate  in  the  sub- 

clavian. 
Receive  blood  from  the  veins  and  sinuses  of  the 

cranial  cavity. 
Begin  at  base  of  skull,  unite  with  subclavian. 


External 

r« 
§     §* 

Jugular 

>  2 

VH      f^ 

Veins 

O    ^^       ' 

CX    rt 

Internal 

5° 

Jugular 

I       Veins 

Q 

226 


ANATOMY  AND   PHYSIOLOGY        [CHAP.  XI 


[ 

r 

Axillary 
Veins 

I 

o 

S 

iuperior  Ve 

Sub- 
clavian 

m 

Veins 

Innominate 

Veins 

Superior 

Vena 
Cava 

Thoracic  Veins  — 

(2) 


Receive  blood  from 
ficial  veins 


super- 


Femoral 
Veins 


External 
Iliacs 

Internal 
Iliacs 

Common 
Iliacs 

Inferior 
Vena 
Cava 


(1)  Receive  blood  from  the  deep  veins  of  the  forearm 

and  arm. 

They  accompany  the  arteries  and  are  called  by 
the  same  names. 

Radial. 

Posterior  ulnar. 
Anterior  ulnar. 
Common  ulnar. 
Median. 
Median  basilic. 
Median  cephalic. 
Basilic. 
Cephalic. 
Formed  by  union  of  the  inner  brachial  and  basilic, 

end  in  the  subclavian. 

Continuation  of  axillary  from  first  rib  to  the  joint  be- 
tween the  sternum  and  clavicle. 
Unite  with  internal  jugular  to  form  innominate. 
Transmit  blood  from  head,  neck,  upper  limbs,  and  part 

of  thoracic  wall.     Receive  lymph. 
Formed  by  union  of  internal  jugular  and  subclavian. 
One  on  each  side  of  body. 
Formed  by  union  of  right  and  left  innominate  veins. 

Three  inches  long. 
I  Opens  into  right  auricle. 
Majority  follow  same  course  and  bear  same  name  as 

arteries. 

Continuation  of  the  popliteal  and  extend  from  opening 
in  adductor  magnus  muscle  to  the  inguinal  ligament. 

(1)  Receive  blood  from  deep  veins  of  foot,  leg,  and  thigh. 
They  accompany  the  arteries  and  are  called  by  the 

same  names. 

(2)  Receive  blood  from  the  [ 

superficial  veins,  two  j  Intend  saphenoiis. 

are  important  External  saphenous. 

Continuation  of  femoral  veins.     Extend  from  inguinal 

ligament  to  the  joint  between  sacrum  and  ilium. 
J  Formed  by  union  of  veins  corresponding  to  branches 
(      of  internal  iliac  artery. 

f  Formed  by  union  of  external  and  internal  iliacs.   Extend 
I      from  base  of  sacrum  to  the  fourth  lumbar  vertebra. 
Formed  by  union  of  the  common  iliacs. 
Extends  from    fourth  lumbar  vertebra  to  the  right 

auricle  of  the  heart. 

Receives  many  tributaries  corresponding   to    arteries 
given  off  from  the  aorta. 


CHAP.  XT] 


SUMMARY 


227 


Supplement- 
ary 
Channel 


Portal  Cir- 
culation 


1.  Right  azygos  vein 

2.  Left  lower  azygos  vein 

3.  Left  upper  azygos  vein 


Connect  with  superior  vena 
cava  above,  and  inferior 
vena  cava  below. 


Portal 
Vein 


Splenic  vein  and  superior 
mesenteric  vein 


Gastric  vein  and  inferior 
mesenteric  vein 


Unite     to     form 

portal  vein. 
Empty   into    the 
portal  vein  be- 
fore   it    enters 
the'  liver. 

Carries  blood  to  liver,  breaks  up  into  capil- 
laries,  then  unites  with  capillaries  from 
hepatic  artery  to  form  hepatic  vein. 
Hepatic  Vein  —  empties  into  inferior  vena  cava. 


CHAPTER  XII 

THE  VASCULAR  SYSTEM  CONTINUED:  THE  GENERAL  CIRCULA- 
TION; BLOOD  PRESSURE;  THE  PULSE;  LYMPH;  FCETAL 
CIRCULATION 

THE    GENERAL   CIRCULATION    OF   THE    BLOOD 

THE  blood  is  contained  in  a  closed  set  of  tubes  which  it  com- 
pletely fills.  Interposed  in  this  set  of  tubes  is  the  heart  which  fills 
with  blood  from  the  veins  and  then  contracts,  thereby  forcing  a 
part  of  this  blood  into  the  lungs  and  a  part  to  all  the  rest  of  the 
body. 

To  trace  the  general  circulation,  we  will  begin  with  the  venous 
blood  which  is  returned  to  the  right  auricle  by  the  superior  and 
inferior  venae  cavse.  It  enters  and  fills  the  right  auricle,  and  the 
right  ventricle  which  for  the  time  being  may  be  thought  of  asfa 
single  chamber,  with  the  tricuspid  valve  open.1  Then  the  auricle 
contracts  and  forces  the  blood  over  the  open  valve  into  the  ven- 
tricle, which  has  already  been  passively  filled,  and  now  becomes 
well  distended  by  the  extra  supply.  The  blood  gets  behind  the 
cusps  of  the  tricuspid  valve  and  closes  them.  After  a  brief  pause, 
(possibly  T^tr  of  a  second)  the  ventricle  contracts  and  forces  the 
blood  over  the  open  semilunar  valves  into  the  pulmonary  artery. 
The  pulmonary  artery  divides  into  two  branches  and  carries  the 
blood  to  the  lungs,  where  it  passes  through  the  innumerable  capil- 
laries that  surround  the  alveoli  or  air  sacs  of  the  lungs.  These 
capillaries  unite  to  form  veins,  and  these  unite  to  form  larger  veins, 
until  finally  two  pulmonary  veins  return  the  blood  from  each  lung 
to  the  left  auricle  and  ventricle.  The  left  auricle  now  contracts 
and  forces  the  blood  over  the  open  bicuspid  valve  into  the  left  ven- 
tricle, just  as  described  for  the  right  side  of  the  heart.  The 
bicuspid  valve  is  closed  in  the  same  way  as  the  tricuspid  and  after 

1  It  is  a  mistake  to  think  that  the  blood  all  accumulates  in  the  auricle  before  any 
is  forwarded  to  the  ventricle. 

228 


CHAP.  XII]      THE  GENERAL  CIRCULATION 


229 


a  brief  pause  the  left  ventricle  contracts,  forcing  the  blood  over  the 
open  semilunar  valve,  into  the  aorta.  From  the  aorta  and  its 
branches  the  blood  travels  in  the  capillaries  to  every  part  of  the 
body.  The  capillaries  unite  to  form  veins,  and  finally  the  blood 
is  returned  by  means  of  the  vense  cavse  to  the  right  auricle,  which 
completes  the  circuit. 

The  pulmonary  circulation. — The  lesser  circulation,  from  the 
right  ventricle  to  the  left  auricle,  is  called  the  pulmonary  circula- 


Pulmbnary  artery. 


Superior  cava  or  vein 
from  head  and  neck. 

Right  auricle. 
Inferior  vena  cava- 

Right  ventricle. 


Portal  circulation. 


Second  renal  circu- 
lation. 


Pulmonary  capillaries. 

Pulmonary  veins. 
Aorta. 

Arteries   to  head  and 
neck. 

Left  auricle. 
Left  ventricle. 


Gastric  and  intestinal 
vessels. 


m First  renal  circulation. 


..Systemic  capillaries. 


FIG.  147. — :  DIAGRAM  OF  THE  CIRCULATION.     (Halliburton.) 

tion.  The  purpose  of  the  pulmonary  circulation  is  to  carry  the 
blood  which  has  been  through  the  system,  giving  up  oxygen  and 
collecting  carbon  dioxide,  to  the  air  sacs  of  the  lungs,  where  the 
red  cells  are  recharged  with  oxygen,  and  the  carbon  dioxide  is 
reduced  to  the  standard  amount.  (See  page  261.) 

The  systemic  circulation.  —  The  more  extensive  circulation, 
from  the  left  ventricle  to  all  parts  of  the  body,  and  the  return  to 
the  right  auricle,  is  known  as  the  systemic  circulation.  The  pur- 
pose of  the  systemic  circulation  is  to  carry  oxygen  and  nutritive 
material  to  all  parts  of  the  body,  and  gather  up  waste  products. 

This  double  circulation,  pulmonary  and  systemic,  is  constantly 


230  ANATOMY   AND   PHYSIOLOGY      [CHAP.  XII 

and  simultaneously  going  on,  as  each  half  of  the  heart  is  in  a  lit- 
eral sense  a  force  pump. 

The  heart  as  a  pump.  —  The  muscles 1  of  the  auricles  and  ven- 
tricles are  so  arranged  that  when  they  contract,  they  lessen  the 
capacity  of  the  chambers  which  they  enclose.  When  this  happens 
the  blood  from  the  contracting  chamber  is  expelled  in  the  direc- 
tion of  the  arrows,  since  the  valves  prevent  its  passage  in  the  op- 
posite direction. 

The  first  sign  of  contraction  is  noted  in  the  sinus  tissue  of  the 
right  auricle  —  the  sino-auricular  node  —  which  is  sometimes 
designated  as  the  pace-maker  of  the  heart.  From  this  spot  the 
wave  of  contraction  spreads  over  the  muscles  of  both  auricles. 
These  contract  simultaneously,  driving  the  blood  into  the 
ventricles.  Meanwhile  the  wave  of  contraction  has  passed  from 
the  auricles  to  the  ventricles,  and  now  spreads  over  the  ventricles, 
which  contract  simultaneously. 

The  wave  of  contraction.  —  If  a  stimulus  be  applied  to  one  end 
of  a  muscle,  a  wave  of  contraction  sweeps  on  over  the  entire  tissue. 
It  is  therefore  easy  to  conceive  how  a  wave  of  contraction  can 
sweep  over  the  muscular  tissue  of  the  auricles  which  is  practically 
continuous.  The  question  is  —  how  is  this  wave  transmitted  to 
the  muscular  tissue  of  the  ventricles  which  is  not  continuous  with 
that  of  the  auricles?  The  connecting  pathway  is  furnished  by 
the  auriculo-ventricular  bundle  of  His  which  transmits  the  im- 
pulses and  causes  the  wave  of  contraction  to  spread  over  the  ven- 
tricles. (See  page  180.) 

The  heart-beat.  —  By  a  heart-beat  we  mean  a  coordinated 
contraction  of  the  cardiac  muscle  resulting  in  the  expulsion  of 
blood  from  both  ventricles.  It  consists  of  (1)  an  active  phase  or 
period  of  contraction  called  the  systole,  and  (2)  a  passive  phase 
or  period  of  dilatation  and  rest  2  called  the  diastole.  The  com- 
bination of  the  systole  and  diastole  constitutes  a  cardiac  cycle  and 
corresponds  to  the  heart-beat.  The  heart  of  a  man  at  rest  may 
beat  seventy-two  times  a  minute.  Some  individuals  have  a  lower 
and  others  a  higher  average.  This  rate  may  be  doubled  by  ex- 
ercise. If  we  assume  that  the  heart  beats  75  times  a  minute,  the 
time  required  for  a  cardiac  cycle  is  about  0.8  of  a  second,  and  half 

1  See  page  174  and  Fig.  106. 

2  The  period  of  rest  is  now  often  considered  separately  as  the  diastasis  or  pause 


CHAP.  XII]      THE   GENERAL   CIRCULATION  231 

of  this,  or  Q.4  of  a  second,  represents  the  diastole  or  passive 
phase. 

Heart  sounds  and  murmurs.  —  If  the  ear  be  applied  over  the 
heart,  certain  sounds  are  heard,  which  recur  with  great  regularity. 
The  first  sound  is  a  comparatively  long,  booming  sound ;  the 
second,  a  short,  sharp,  sudden  one.  The  sounds  resemble  the 
syllables '  lubb  dup.  The  first  sound  is  thought  to  be  due  to  vi- 
brations caused  by  the  closure  of  the  auriculo-ventricular  valves 
and  the  contraction  of  the  ventricles ;  the  second  is  attributed  to 
vibrations  set  up  by  the  sudden  closure  of  the  semilunar  valves. 
In  certain  diseases  of  the  heart  these  sounds  become  changed  and 
obscure,  and  are  called  murmurs.  These  are  often  due  to  failure  of 
the  valves  to  close  properly,  thus  allowing  regurgitation  of  the  blood. 

Cause  of  the  heart-beat.  —  The  cause  of  the  heart-beat  is  still  an 
unsettled  question.  We  do  not  know  whether  the  rhythmic  con- 
tractions are  due  to  the  nerve  tissue  which  the  heart  contains,  or 
whether  they  are  due  to  a  power  inherent  in  the  muscle  itself. 
The  results  of  many  experiments  support  the  theory  that  the  func- 
tion of  the  nerve  tissue  is  regulatory;  that  the  contractions  are 
due  to  the  inherent  power  of  automaticity,  and  that  the  stimulus 
which  excites  the  contractions  is  a  chemical  one  dependent  upon 
the  presence  of  definite  proportions  of  certain  salts  in  the  blood. 
It  has  been  shown  that  all  the  constituents  of  the  blood  can  be 
dispensed  with  except  water  and  these  essential  salts,  i.e., 
sodium  chloride  0.9  per  cent,  calcium  chloride  0.024  per  cent, 
and  potassium  chloride  0.042  per  cent.1  Under  normal  con- 
ditions these  salts  are  always  present,  and  as  the  blood  is  con- 
stantly passing  through  the  heart,  it  follows  that  the  heart  is 
subjected  to  a  continuous  stimulus.  It  is  natural  to  question 
why  the  heart  is  not  in  a  state  of  continuous  contraction?  In 
other  words,  how  is  relaxation  possible?  In  answer  it  may  be 
stated  that  as  soon  as  the  heart  has  contracted  it  loses  its  irri- 
tability to  every  sort  of  stimulus  and  relaxes.  After  a  time  its 
irritability  returns  and  it  reaches  a  condition  in  which  it  is  again 
able  to  respond  to  a  stimulus  and  contracts  again.  Each  con- 
traction is  followed  by  a  period  of  relaxation  known  as  the  refractory 
period.  Thus  the  rhythmic  action  of  the  heart  is  due  to  the 
refractory  period. 

1  A  solution  of  this  composition  is  known  as  Ringers'  solution. 


232  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XII 

Automaticity .  —  The  most  remarkable  power  of  cardiac  muscle 
is  its  automaticity.  Skeletal  muscle  rarely  contracts  except  in 
response  to  the  arrival  of  stimuli  by  way  of  the  motor  nerves. 
Visceral  muscle  shows  an  automatic  tendency,  but  this  power  is 
most  highly  developed  in  the  heart.  This  may  be  demonstrated 
by  removing  the  heart  of  a  frog  from  the  body  of  the  animal. 
The  heart  will  continue  to  beat  for  hours  provided  it  is  kept  moist 
with  Ringers'  solution.  The  degree  of  automatic  power  pos- 
sessed by  different  regions  of  the  heart  varies.  Some  parts  beat 
faster  than  others.  The  most  rapidly  contracting  part  is  the  sino- 
auricular  node  of  the  right  auricle.  It  is  from  this  particular  spot 
that  the  wave  of  contraction  radiates,  and  from  here  it  is  trans- 
mitted over  the  bundle  of  His  to  the  ventricles.  Ordinarily,  the 
ventricles  beat  at  the  rate  set  by  the  right  auricle,  but  if  for  any 
reason  the  auricle  ceases  to  beat,  the  ventricles  will  beat  inde- 
pendently but  at  a  slower  rate.1  Thus  the  normal  sequence  of 
the  contraction  depends  upon  the  fact  that  the  automaticity  of 
the  right  auricle  is  more  highly  developed  than  that  of  the  ven- 
tricles. 

Nervous  control  of  the  heart.  —  Although  the  heart  contracts 
automatically  and  rhythmically,  it  is  under  normal  conditions 
controlled  by  two  sets  of  nerves.  These  consist  of  inhibitory  nerves 
coming  to  the  heart  from  the  pneumogastric  or  vagus  nerve,  and 
accelerator  nerves  from  the  sympathetic  system.  The  inhibitory 
nerves  have  their  cell-bodies  situated  in  the  medulla  where  they 
form  a  cardio-inhibitory  centre.  The  location  of  the  cardio-accel- 
erator  centre  has  not  been  determined.  Both  the  inhibitory  and 
accelerator  nerves  are  in  a  state  of  constant,  though  slight,  ac- 
tivity. This  means  that  the  heart-beat  is  controlled  by  two 
antagonistic  influences,  one  tending  to  slow  the  heart  action,  and 
the  other  to  quicken  it.  If  the  inhibitory  centre  is  stimulated  to 
greater  activity,  the  heart  is  slowed  still  further.  If  this  center 
is  inhibited,  the  heart-rate  is  increased,  because  the  inhibitory 
action  is  removed.  Stimulation  of  the  accelerator  nerves  results 
in  a  quickened  heart-beat,  and  section  of  these  nerves  slows  the 
heart. 

1  Experimentally  the  bundle  of  His  may  be  damaged,  with  the  result  that  the 
auricles  beat  as  before,  but  the  ventricles  adopt  a  slower  rate,  thus  creating  a  condi- 
tion known  as  heart-block. 


CHAP.  XII]      THE   GENERAL   CIRCULATION  233 

Factors  maintaining  arterial  circulation.  —  The  most  important 
factors  maintaining  arterial  circulation  are  (1)  the  pumping  action 
of  the  heart,1  (2)  the  extensibility  and  elasticity  of  the  arterial 
walls,  and  (3)  the  peripheral  resistance. 

The  extensibility  and  elasticity  of  the  arterial  walls.  —  Each 
time  the  ventricles  contract  they  force  a  certain  amount  of  blood 
into  arteries  that  are  already  full.2  The  extensibility  of  the  ar- 
teries enables  them  to  distend  and  receive  this  extra  supply  of 
blood.  This  period  of  distention  corresponds  to  the  contraction 
period  of  the  heart.  Just  as  soon  as  the  force  is  removed,  the  elas- 
ticity of  the  arteries  causes  them  to  contract,  and  exerts  such  a 
pressure  on  the  contained  blood,  that  this  blood  is  forced  into  the 
capillaries  just  rapidly  enough  to  allow  the  arteries  time  to  reach 
their  usual  size  by  the  beginning  of  the  next  contraction  period 
of  the  heart.  They  thus  serve  not  only  as  conducting  tubes  but 
exert  a  force  that  assists  the  heart  in  driving  the  blood  into  the 
capillaries. 

The  extensibility  and  elasticity  of  the  arteries  change  with  the 
health  and  age  of  the  individual.  Sometimes  as  the  result  of  dis- 
ease, and  always  as  we  grow  older,  the  arterial  walls  grow  stiffer 
and  more  rigid,  and  become  less  well  adapted  for  the  unceasing 
work  they  are  called  upon  to  perform.  This  condition  is  known  as 
arteriosclerosis. 

Peripheral  resistance.  —  This  term  is  used  to  designate  the  re- 
sistance offered  by  the  innumerable  arterioles  and  capillaries  into 
which  the  large  arteries  empty.  It  is  easy  to  realize  that  a  large 
tube  like  the  aorta  offers  less  resistance  to  the  flow  of  blood, 
than  an  enormous  number  of  microscopic  tubes  like  the  capil- 
laries. 

Factors  maintaining  venous  circulation.  —  The  effect  of  the 
pumping  action  of  the  heart  is  not  entirely  spent  in  forcing  the 
blood  through  the  arteries  and  capillaries.  A  little  force  still 
remains  to  propel  the  blood  back  to  the  heart  again,  and  the  pres- 
ence of  valves  keeps  it  flowing  in  the  right  direction,  i.e.,  toward 
the  heart.  The  return  flow  is  also  favored  by  (1)  the  suction  action 
of  the  heart  caused  by  the  emptying  of  the  auricles,  (2)  the  heart 
and  respiratory  movements  which  cause  continual  changes  of 
pressure  in  the  thorax  and  abdomen,  (3)  the  contractions  of  the 

1  See  page  230.  J  Estimated  all  the  way  from  2  to  6  ounces. 


234 


ANATOMY   AND    PHYSIOLOGY      [CHAP.  XII 


skeletal  muscles  which  exercise  a  massaging  action  upon  the  veins, 
and  aided  by  the  valves,  propel  the  blood  toward  the  heart. 

The  velocity  of  the  blood-flow.  —  In  all  the  large  arteries  the 
blood  moves  rapidly;  in  the  capillaries  very  slowly;  and  in  the 
veins  the  velocity  is  augumented  as  they  increase  in  size,  but  never 
equals  that  in  the  aorta.  The  underlying  principle  is  that  in  any 


CAPILLARIES 


FIG.  148.  —  DIAGRAM  TO  ILLUSTRATE  VARIATIONS  IN  VELOCITY  OF  BLOOD 
FLOW.  If  a  vessel  divides  into  two  branches,  these  will  be  individually  of  less  cross- 
section  than  the  main  trunk,  but  united  they  will  exceed  it.  Linear  velocity  will 
be  lower  in  the  branches  than  in  the  parent  stock.  The  sum  of  the  cross-sectional 
areas  of  the  capillaries  is  greater  than  that  of  the  artery  or  vein. 

stream  the  velocity  is  greatest  where  the  cross-section  of  the  channel 
is  least,  and  lowest  where  the  cross-section  is  greatest..  The 
application  of  this  principle  requires  that  we  regard  the  aorta  as 
the  narrowest  and  the  capillaries  as  the  widest  part  of  the  vascular 
system.  This  is  readily  admitted  if  we  remember  that  it  is  the 
combined  channels  of  millions  of  capillaries  which  we  have  to  com- 
pare with  the  aorta.  It  is  a  generally  accepted  truth  that  when  a 
vessel  divides,  the  sum  of  the  cross-sections  of  the  two  branches 
is  greater  than  that  of  the  main  trunk.  Consequently  the  velocity 
will  be  reduced  when  an  artery  divides,  and  increased  when  two 
veins  unite  to  make  one.  The  reason  why  the  velocity  in  the 
veins  never  equals  that  in  the  aorta  is  because  the  cross-section 
of  the  two  venae  cavse  is  greater  than  the  cross-section  of  the 
single  aorta.  The  actual  service  of  the  blood  to  the  tissues  is 
rendered  in  the  capillaries  (since  the  walls  of  the  arteries  and 
veins  are  too  thick  to  permit  of  diffusion),  hence  the  value  of  the 
slow  passage. 


CHAP.  XII]  BLOOD   PRESSURE  235 

Distribution  of  blood  to  different  parts  of  the  body.  —  The  quantity 
of  blood  contained  in  the  body  is  always  about  the  same,  but  the 
distribution  varies,  and  is  determined  by  the  needs  of  the  different 
parts.  When  the  digestive  organs  are  active,  they  need  an  extra 
supply  of  blood,  which  is  furnished  by  depleting  the  quantity  in 
less  active  organs,  i.e.,  the  muscles  or  skin.  On  the  other  hand, 
active  muscular  work  requires  that  an  increased  supply  of  blood 
be  sent  to  the  muscles  and  lungs  and  less  to  the  digestive  organs. 


BLOOD   PRESSURE 

By  blood  pressure  is  meant  the  pressure  the  blood  exerts  against 
the  walls  of  the  vessels  in  which  it  is  contained.  The  term  includes 
arterial,  capillary,  and  venous  pressure.  A  vein  is  easily  flattened 
under  the  finger ;  an  artery  offers  a  stronger  resistance.  This  is  an 
indication  of  a  great  difference  between  arterial  and  venous  pres- 
sure. This  difference  is  also  shown  when  an  artery  and  a  vein  are 
cut ;  the  blood  springs  from  the  artery  in  a  pulsating  spurt,  while 
the  flow  from  the  vein  is  continuous  and  even  when  copious  "  wells 
up  "  rather  than  "  spurts  out." 

Various  experiments  have  put  us  in  possession  of  the  following 
facts.  Pressure  in  the  arteries  is  high  and  fluctuating,  slightly 
higher  in  the  large  trunks  than  in  their  branches ;  pressure  in  the 
veins  is  low  and  relatively  constant.  It  must  be  higher  in  the 
small  veins  than  in  the  large  ones  they  unite  to  form,  because  the 
direction  of  the  blood-flow  is  from  the  smaller  to  the  larger  ones. 

When  the  blood  leaves  the  left  ventricle  the  high  pressure  which 
it  exerts  against  the  wall  of  the  aorta  may  be  regarded  as  a  measure 
of  energy.  This  energy  is  transformed  into  heat  in  overcoming 
the  friction  encountered  in  the  vessels.  When  the  blood  reaches 
the  capillaries,  the  surface  is  multiplied  and  the  friction  increased, 
This  offers  an  impediment  to  the  flow,  and  the  result  is  a  decided 
drop  in  the  pressure. 

Arterial  pressure  is  not  uniform,  but  varies  (1)  with  the  systole 
and  diastole  of  the  heart,  being  greater  during  the  systole ;  (2)  it 
is  less  in  youth,  and  increases  as  we  grow  older,,  because  the  arteries 
are  less  elastic ;  (3)  conditions  of  health  may  affect  the  normal 
muscular  tone  of  the  arteries  and  heart.  When  the  arteries  lose 
their  tone,  or  the  heart-beat  loses  its  force,  the  blood  pressure  is 


236 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XII 


low.     When  the  arteries  are  overconstricted,  or  the  heart  over- 
stimulated,  the  blood  pressure  is  high. 

Method  of  determining  blood  pressure.  —  It  is  customary  to 
try  the  pulse  at  the  wrist  to  determine  whether  the  patient  has 


B 

FIG.  149.  —  SPHYGMOMANOMETERS.     A,  the  mercury  instrument    is    accurate, 
although  a  trifle  more  bulky  than  the  spring  type.     B,  the  spring  type  of  instrument. 


CHAP.  XII]  BLOOD   PRESSURE  237 

high  blood  pressure.  If  the  radial  artery  is  hard  and  incom- 
pressible it  may  indicate  either  that  some  change  has  occurred 
in  the  vessel,  or  that  the  pressure  is  high.  If,  however,  the 
pulse  is  easy  to  obliterate  with  the  fingers  it  is  usual  to  find  a 
low  pressure. 

Of  late  years  many  forms  of  apparatus  have  been  devised  by 
which  a  more  accurate  knowledge  of  this  condition  can  be  ob- 
tained. This  apparatus  is  called  a  sphygmomandtneter,  and  con- 
sists of  a  scaled  column  of  mercury  which  is  connected  with  an 
air  bag  by  rubber  tubing.  The  air  bag  is  in  turn  connected 
with  a  small  hand  pump  and  is  contained  in  a  cuff  of  either 
leather  or  cloth.  Some  instruments  are  constructed  with  a 
spring  scale  instead  of  a  column  of  mercury  but  the  principle  is 
the  same. 

The  air  bag  contained  in  the  cuff  is  buckled  snugly  about  the 
arm  just  above  the  elbow  so  as  to  compress  the  brachial  artery. 
By  placing  the  finger  upon  the  pulse  at  the  wrist  (as  we  inflate  the 
bag) ,  we  finally  reach  a  point  where  the  pulse  disappears,  or  in  other 
words,  the  pressure  in  the  bag  as  indicated  on  the  instrument  is 
equal  to  the  pressure,  which  is  necessary  to  overcome  the  pressure 
of  the  artery  wall,  plus  the  force  of  the  heart-beat.  This  is  known 
as  systolic  pressure.  Another  method  is  to  place  a  stethoscope 
over  the  brachial  artery  (instead  of  the  hand  on  the  pulse) ,  and  note 
the  point  at  which  the  pulse  disappears.  After  the  systolic  pres- 
sure has  been  ascertained  by  releasing  the  air  slightly  in  the  cuff 
and  allowing  the  scale  to  drop,  the  pulse  first  becomes  more  posi- 
tive and  then  fainter  until  it  is  lost  to  the  stethoscope.  The  point 
lowest  on  the  scale  where  it  disappears  is  known  as  the  diastolic 
pressure.  The  diastolic  pressure  cannot  be  taken  by  the  finger- 
pulse  method.  It  is  necessary  to  use  a  stethoscope. 

Normal  degree  of  blood  pressure.  —  The  normal  degree  of  blood 
pressure  necessary  to  obliterate  the  pulse  in  the  brachial  artery 
is  about  11  to  13.5  cm.  (centimetres  of  mercury  column)  for 
systolic,  and  5.5  to  7  cm.  diastolic.  Pressure  varies  with  age, 
and  even  in  health  is  not  constantly  the  same.  Increase  in  the  force 
and  frequency  of  the  heart  increases  the  pressure.  Cold,  drugs, 
etc.  which  constrict  the  arterial  pulse  may  raise  the  blood  pres- 
sure. Heat,  and  the  drugs  of  the  vaso-dilator  group  like  nitro- 
glycerin,  may  lower  it. 


238  ANATOMY  AND  PHYSIOLOGY      [CHAP.  XII 

THE  PULSE 

When  the  finger  is  placed  on  an  artery,  a  sense  of  resistance  is 
felt,  and  this  resistance  seems  to  be  increased  at  intervals,  corre- 
sponding to  the  heart-beat,  the  wall  of  the  artery  at  each  heart- 
beat being  felt  to  rise  up  or  dilate  under  the  finger.  This  alternate 
dilatation  and  contraction  of  the  artery  constitutes  the  pulse; 
and  in  certain  arteries  which  lie  near  the  surface  this  pulse  may  be 
seen  with  the  eye.  When  the  finger  is  placed  on  a  vein,  very  little 
resistance  is  felt;  and,  under  ordinary  circumstances,  no  pulse 
can  be  perceived  by  the  touch  or  by  the  eye. 

As  each  expansion  of  an  artery  is  produced  by  a  contraction  of 
the  heart,  the  pulse,  as  felt  in  any  superficial  artery,  is  a  con- 
venient guide  for  ascertaining  the  character  of  the  heart's 
action. 

Locations  where  the  pulse  may  be  felt.  —  The  pulse  may  be 
counted  wherever  an  artery  approaches  the  surface  of  the  body. 
These  locations  are  :  — 

(1)  The  facial  artery,  where  it  passes  over  the  lower  jawbone. 

(2)  The  temporal  artery,  above  and  to  the  outer  side  of  the 
outer  canthus  of  the  eye. 

(3)  The  brachial  artery,  along  the  inner  side  of  the  biceps  muscle. 

(4)  The  radial  artery,  on  the  thumb  side  of  the  wrist.     On  ac- 
count of  its  accessible  situation  the  radial  artery  is  usually  em- 
ployed for  this  purpose. 

(5)  The  femoral  artery,  where  it  passes  over  the  pelvic  bone. 

(6)  The*  dor  sails  pedis,  on  the  dor  sum  of  the  foot. 

Points  to  note  in  feeling  a  pulse.  —  In  feeling  a  pulse  the  follow- 
ing points  should  be  noted. 

(1)  Frequency,  or  the  number  of  pulse-beats  per  minute. 

(2)  Strength,  or  the  force  of  the  heart-beat. 

(3)  Regularity,  or  the  same  number  of  beats  per  minute. 

(4)  Equality.  —  Each  beat  should  have  the  same  force,   not 
some  strong  and  some  weak.     It  sometimes  happens  that  a  beat  is 
missed  because  the  heart-beat  is  too  weak  to  distend  the  artery. 
This  is  called  an  intermittent  pulse. 

Occasionally  there  is  a  lack  of  tone  in  the  arterial  walls  and  a 
dicrotic  pulse  is  felt.  This  means  that  the  pulsations  are  divided 
and  the  second  part  of  the  beat  is  weaker  than  the  first. 


CHAP.  XII]  THE   LYMPH  239 

(5)  Blood  pressure.  —  This  is  suggested  by  the  amount  of  force 
that  is  required  to  obliterate  the  pulse. 

Average  frequency  of  the  pulse. — The  average  frequency  of 
the  pulse  in  man  is  seventy-two  beats  per  minute.  This  rate  may 
be  increased  after  eating  or  by  muscular  action.  Even  the  varia- 
tion of  the  muscular  effort  entailed  between  the  standing,  sitting, 
and  recumbent  positions  will  make  a  difference  in  the  frequency 
of  the  pulse  of  from  eight  to  ten  beats  per  minute.  Mental  excite- 
ment may  also  produce  a  temporary  acceleration,  varying  in 
degree  with  the  peculiarities  of  the  individual.  Age  has  a  marked 
influence.  At  birth  the  pulse  rate  is  about  130  per  minute;  at 
three  years,  100;  in  adult  life,  72;  in  old  age,  65.  It  is  some- 
what more  rapid  in  women  than  in  men  and  is  lowered  during 
sleep.  Idiosyncrasies  are  frequently  met  with.  A  person  in 
perfect  health  may  have  a  much  higher  or  a  much  lower  rate  than 
72.  The  relative  frequency  of  the  pulse  and  respirations  is  about 
four  heart-beats  to  one  respiration. 

As  a  rule,  the  rapidity  of  the  heart's  action  is  in  inverse  ratio 
to  its  force.  An  infrequent  pulse,  within  physiological  limits, 
is  usually  a  strong  one,  and  a  frequent  pulse  comparatively  feeble ; 
the  pulse  in  fever  or  debilitating  affections  becoming  weaker  as  it 
grows  more  rapid. 

LYMPH 

Formation  of  lymph.  —  The  lymph  is  derived  from  the  blood 
in  the  capillaries,  but  the  exact  process  is  still  an  open  question. 
It  is  considered  probable  that  it  is  partly  a  process  of  filtration 
which  depends  on  the  permeable  nature  of  the  walls  of  the  capil- 
laries, and  partly  the  result  of  a  secretory  process  on  the  part  of 
the  endothelial  cells  lining  the  capillaries.  The  filtration  theory 
is  supported  by  the  fact  that  the  blood  in  the  capillaries  is  under 
greater  pressure  than  in  the  arteries  or  veins.  The  secretory  pro- 
cess is  supported  by  the  chemical  differences  between  the  blood 
and  the  lymph. 

Factors  controlling  the  flow  of  lymph.  —  The  onward  progress 
of  the  lymph  from  the  tissues  to  the  veins  is  maintained  chiefly 
by  three  things. 

(1)  Differences  in  pressure.  —  The  lymph  in  the  tissue  spaces 
is  under  greater  pressure  than  the  lymph  in  the  lymph  capillaries, 


240  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XII 

and  the  pressure  in  the  larger  lymphatics  near  the  ducts  is  much 
less  than  in  the  smaller  vessels.  Consequently  we  may  consider 
that  the  lymphatics  form  a  system  of  vessels  leading  from  a 
region  of  high  pressure,  viz.  the  lymph  spaces  of  the  tissues,  to  a 
region  of  low  pressure,  viz.  the  interior  of  the  large  veins  of  the 
neck. 

(2)  Muscular  movements  and  valves.  —  The  muscular  move- 
ments of  the  body  compress  the  lymphatics  and  force  the  lymph 
on   in   the  proper  direction.     The   numerous   valves   prevent   a 
return  flow  in  the  wrong  direction. 

(3)  Respiration.  —  During  each  inspiration  the  pressure  on  the 
thoracic  duct  is  less  than  on  the  lymphatics  outside  the  thorax, 
and  the  lymph  is  accordingly  "  sucked  "  into  the  duct.     During 
the  succeeding  expiration  the  pressure  on  the  thoracic  duct  is  in- 
creased, and  some  of  its  contents,  prevented  by  the  valve  from 
escaping  bejow,  are  pressed  out  into  the  innominate  veins. 

(Edema.  —  The  lymph  in  the  various  lymph  spaces  of  the  body 
varies  in  amount  from  time  to  time,  but  under  normal  circum- 
stances never  exceeds  certain  limits.  Under  abnormal  condi- 
tions, these  limits  may  be  exceeded,  and  the  result  is  known  as 
oedema,  or  dropsy.  Similar  excessive  accumulations  may  also 
occur  in  the  larger  lymph  spaces,  the  serous  cavities. 

Among  the  possible  causes  of  oedema  are :  — 

(1)  An  excessive  formation,  the  lymph  gathering  in  the  lymph 
spaces  faster  than  it  can  be  carried  away  by  a  normal  flow. 

(2)  Any  obstruction  to  the  flow  of  lymph  from  the  lymph  spaces. 

FCETAL  CIRCULATION 

Certain  structures  are  necessary  to  the  performance  of  fcetal 
circulation,  but  are  of  no  use  after  birth.  They  are  as  follows  :  - 

(1)  Foramen  ovale. — An  opening  between  the  two  auricles. 
It  furnishes  direct  communication  between  them. 

(2)  Ductus  arteriosus.  —  A  blood-vessel  connecting  the  aorta 
and  pulmonary  artery. 

(3)  Ductus  venosus.  —  A  blood-vessel  connecting  the  umbilical 
vein  and  the  inferior  vena  cava. 

(4)  The   placenta   and   umbilical   cord.  —  The  placenta   is  a 
ir.ass  of   tissue  rich   in  blood-vessels  which  is  in  close  contact 


CHAP.  XII]        THE  FCETAL  CIRCULATION 


241 


with  the  lining  of 
placenta  with  the 
of  two  arteries  and 
one  large  vein  pro- 
tected by  Wharton's 
jelly.  The  arteries 
are  branches  of  the 
arterial  system  of 
the  foetus,  and  carry 
blood  from  the  foetus 
to  the  placenta 
where  it  is  sepa- 
rated by  the  thin- 
nest of  walls  from 
the  maternal  blood 
in  the  blood-vessels 
of  the  uterus.  The 
usual  distinctions 
between  arterial  and 
venous  blood  cannot 
be  recognized,  as  the 
blood  of  the  foetus 
is  never  up  to  the 
arterial  standard  of 
the  mother.  The 
best  blood  is  that 
which  has  been  im- 
proved by  effecting 
exchanges  with  the 
blood  in  the  uterine 
vessels,  and  is  car- 
ried from  the  pla- 
centa to  the  foetus 
by  the  vein.  By 
means  of  the  pla- 
centa the  foetus  ob- 
tains oxygen,  but 
it  is  more  than  a 
lung;  it  is  the  seat 


the  uterus.     The  umbilical  cord  unites  the 
navel  of  the  child.     The  cord   is  made  up 


A* 


|      "]      ARTERIAL  BLOOD 
$M      VENOUS    BLOOD 


FIG.  150.  —  DIAGRAM  OF  CIRCULATION  BEFORE 
BIRTH.  Foetal  type.  The  arrows  indicate  the  course 
of  the  blood.  (Cooke.) 


242  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XII 

of  the  absorption  of  food,  and  serves  for  the  unloading  of 
wastes. 

Course  of  the  blood.  —  The  blood  is  carried  from  the  placenta 
along  the  umbilical  cord  by  the  umbilical  vein.  Entering  the 
foetus  it  is  conveyed  into  the  ascending  vena  cava  partly  through 
the  liver  but  chiefly  through  the  ductus  venosus,  which  con- 
nects these  two  vessels.  From  the  ascending  vena  cava  it  enters 
the  right  auricle,  passes  through  the  foramen  ovale  into  the  left 
auricle,  thence  into  the  left  ventricle,  and  out  through  the  aorta, 
which  distributes  it  principally  to  the  upper  extremities.  The 
blood  from  the  head  and  upper  extremities  returns  by  the  descend- 
ing vena  cava  to  the  right  auricle,  then,  passes  into  the  right  ven- 
tricle, and  out  through  the  pulmonary  artery  to  the  lungs.  As 
the  lungs  in  the  fcetus  are  solid,  they  require  very  little  blood 
(only  for  nutrition),  and  the  greater  part  of  the  blood  passes 
through  the  ductus  arteriosus  into  the  descending  aorta,  where, 
mixing  with  the  blood  delivered  to  the  aorta  by  the  left  ventricle, 
it  descends  to  supply  the  lower  extremities  of  the  foetus.  The 
chief  portion  of  this  blood  is  carried  to  the  placenta  by  the  two 
umbilical  arteries,  but  a  small  amount  passes  back  into  the  as- 
cending vena  cava  and  mixes  with  the  blood  from  the  placenta. 

From  this  description  of  the  foetal  -circulation,  it  follows :  — 

1.  That  the  placenta  serves  the  purpose  of  a  respiratory,  nu- 
tritive, and  excretory  organ. 

2.  That  the  liver  receives  blood  directly  from  the  placenta; 
hence  the  large  size  of  this  organ  at  birth. 

3.  That  the  blood  from  the  placenta  passes  almost  directly 
into  the  arch  of  the  aorta,  and  is  distributed  by  its  branches  to 
the  head  and  upper  extremities ;  hence  the  large  size  and  perfect 
development  of  these  parts  at  birth. 

4.  That  the  blood  in  the  descending  aorta  is  chiefly  derived 
from  that  which  has  already  circulated  in  the  upper  extremities, 
and,  mixed  with  only  a  small  quantity  from  the  left   ventricle, 
is  distributed  to  the  lower  extremities ;   hence  the  small  size  and 
imperfect  development  of  these  parts  at  birth. 

Changes  in  the  vascular  system  at  birth.  —  From  the  foregoing 
description  it  is  obvious  that  at  birth  very  important  changes  must 
take  place :  — 

1.  The  blood  clots  in  the  umbilical  vein,  between  the  usual 


CHAP.  XII]         THE  FCETAL   CIRCULATION  243 

ligature  and  the  liver,  also  in  the  ductus  venosus.     The  blood  clot 
becomes  organized  and  these  two  vessels  become  obliterated. 

2.  As   respiration   commences,    the   blood   traverses   the   pul- 
monary arteries,  and  then  returns  to  the  heart  by  the  pulmonary 
veins ;  this  raises  the  blood  pressure  in  the  left  auricle,  and  causes 
the  valve  over  the  foramen  ovale  to  close. 

3.  The  blood  in  the  ductus  arteriosus  clots,  the  clot  organizes, 
and  the  ductus  arteriosus  becomes  a  fibrous  cord. 

4.  The  blood  in  the  hypogastric  arteries  also  clots,  the  clots 
organize,  and  these  vessels  become  obliterated. 

Occasionally  some  of  the  embryonic  by-passes  fail  to  close,  and 
so  much  venous  blood  enters  the  arterial  system  that  a  blue 
baby  is  the  result.  In  such  instances  the  child  suffers  from 
malnutrition  and  the  chances  for  survival  are  slight. 


244 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XII 


Pulmonary 

Circulation 

General 

Circulation  < 

Systemic 

Circulation 

Heart 


Pumping 
Action 

Wave  of 
Contrac- 
tion 


Heart 
Beat 


Heart 
Sounds 


SUMMARY 

Right  auricle  to  right  ventricle,  then  pulmonary 
arteries   to   lungs.     Capillary   system.     Re- 
turn by  pulmonary  veins  to  left  auricle. 
Purpose  —  To   increase  oxygen  and  decrease 

carbon  dioxide  to  standard  amount. 
Left  auricle  to  left  ventricle,  then  by  means  of 
aorta  and  its  branches  to  all  parts  of  the  body. 
Capillary  system.     Return  by  veins  which 
empty  into  superior  and  inferior  venae  cavae. 
Carry,  and     Oxygen. 

give  up  to     Nutritive       ma- 
Purpose        ^      the  cells  terials. 

Take    from     f  Carbon  dioxide, 
the  cells       [  Waste  products. 

f  Muscles  contract  and  lessen  capacity  of  auricles 
<  and  ventricles,  thus  forcing  blood  into 
I  arteries. 

{Starts  at  sino-auricular  node,  transmitted  to 
bundle  of  His,  which  in  turn  transmits  it  to 
the  ventricles. 
Coordinated  contraction  of  cardiac  muscle. 

Cardiac    cycle,     72 


Systole  —  Active  stage 
Diastole  —  Passive  stage 


per  minute. 
Occupies  about  0.8 

of  a  second, 
inherent       in      heart 


Automaticity 
muscle. 

f  Sodium. 

Stimulated  by  chlorides  I  Potassium. 
Cause  [  [  Calcium. 

Vagus    nerve  —  inhibi- 
tory. 

Sympathetic     system  — 
accelerator. 

{Vibrations  caused  by  closure  of  auric- 
ulo-ventricular  valves  and  the  con- 
traction of  ventricles. 

Dup  —  Vibrations  caused  by  closure  of  semi- 
lunar  valves. 


Innervation 
is  regu- 
latory. 


Factors 
Maintaining 
Arterial 
Circulation 


1.  Pumping  action  of  the  heart. 

2.  The  extensibility  and  elasticity  of  the  arterial  walls. 

3.  Peripheral  resistance. 


CHAP.  XII] 


SUMMARY 


245 


Factors 
Maintaining 
Venous 
Circulation 


Velocity  of 
Blood-flow 


Blood 
Pressure 


Pulse 


1.  Some  force  due  to  pumping  action  of  the  heart. 

2.  Suction  action  of  the  heart. 

3.  Changes  of  pressure  in  thorax  and  abdomen  due  to  heart 

and  respiratory  movements. 

4.  Contractions  of  the  skeletal  muscles. 

Arteries  —  blood  moves  rapidly  in  large  arteries,   more 

slowly  in  smaller  ones. 
Capillaries  —  blood  moves  very  slowly. 
Veins  —  blood  moves  slowly  in  small  veins,  more  rapidly 

in  larger  veins,  but  never  as  rapidly  as  in  arteries. 

Pressure  blood  exerts  against  walls  of  vessels. 
High  and  fluctuating. 

1.  Higher  during  systole. 

2.  Lower  during  diastole. 

3.  Increases  with  age. 


Arterial 


4. 


Not  uniform 

Decreases  if  heart  or  arteries 

lose  their  tone. 
Venous  —  Low  and  constant. 

1 .  Scaled  column  of  mercury 
with 


Determined  by  use  of  sphyg- 
momanometer 


connected 


air 


Normal 


2.  An  air  bag  contained  in  a 

cuff  of  leather  or  cloth. 

3.  Air   bag    also    connected 

with  hand  pump. 
f  Systolic  or  maximum  —  11.0  to  13.5  cm. 
1  Diastolic  or  minimum  —  5.5  to  7.0  cm. 


Alternate  contraction  and  expansion  of  artery. 


Locations 
where  Pulse 
may  be 
Counted 


Points  to  Note 


Pulse  Rate 


Facial  artery. 
Temporal  artery. 
Brachial  artery. 
Radial  artery. 
Femoral  artery. 
Dorsalis  pedis. 
Frequency. 
Strength. 
Regularity. 
Equality. 
Blood  pressure. 
Infant,  130 
Three  years,  100 
Adult,  72 
Old  age,  65 


Higher  in  women 
than  in  men. 


246 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  XII 


Pulse 


Lymph  .     . 


(Edema 


Foetal 
Circulation 


Changes  in 
Vascular  System 
at  Birth 


Changes  in 
Pulse  Rate 
may  be  Due 
to 


Formation 


Eating. 

Muscular  activity. 
Mental  excitement. 
Age. 
Sleep. 

Condition  of  health. 
Idiosyncrasies. 
Process  of  filtration. 
Process  of  secretion. 
Factors  Con-      [  Differences  in  pressure. 

trolling  Flow  <  Muscular  movements  and  valves. 
[  Respiration. 

Accumulation  of  lymph  in  tissues. 

f  1.  Excessive  formation. 
May  be  d    2    Obgtmction  to  flow  of  lymph  from 

tissue. 

1.  Direct  communication  between  right  and  left  auricle 

by  means  of  foramen  ovale. 

2.  Direct  communication  between  umbilical  vein  and 

inferior  vena  cava.     Ductus  venosus. 

3.  Direct  communication  between  pulmonary  artery 

and  aorta.     Ductus  arteriosus. 

4.  Oxygen  and  nutritive   substances   obtained  from 

placenta. 

1.  Umbilical  vein  and  ductus  venosus  become  obliter- 

ated. 

2.  Respiration  stimulates  pulmonary  circulation ;   this 

raises  the  blood  pressure  in  left  auricle,  and  closes 
foramen  ovale. 

3.  Ductus  arteriosus  becomes  a  fibrous  cord. 

4.  Hypogastric  arteries  become  obliterated. 


CHAPTER  XIII 

RESPIRATORY  SYSTEM:  NOSE;  LARYNX;  TRACHEA;  BRONCHI; 
LUNGS.  —  RESPIRATION ;  ABNORMAL  TYPES  OF  RESPIRA- 
TION. MODIFIED  RESPIRATORY  MOVEMENTS 

THE  process  of  respiration  is  dependent  upon  the  proper  func- 
tioning of  certain  organs,  which  we  group  together  and  call  a  res- 
piratory system.  The  essentials  of  a  respiratory  system  consist 
of  a  moist  and  permeable  membrane,  with  a  moving  stream  of 

AIR 

THfN  MUCOSA    I         -          I I 1         — I ^~ 


CAPILLARY  BLOOD  VESSEL 


FIG.  151.  —  DIAGRAM  OF  THE  ESSENTIALS  OF  A  RESPIRATORY  SYSTEM. 

(Gerrish.) 

blood  containing  a  high  percentage  of  carbon  dioxide  on  one  side, 
and  air  or  fluid  containing  a  high  percentage  of  oxygen  on  the  other. 
In  most  aquatic  animals  the  respiratory  organs  are  external  in  the 
form  of  gills ;  in  terrestrial,  or  air-breathing  animals,  the  respira- 
tory organs  are  situated  internally  in  the  form  of  lungs,  and  are 
placed  in  communication  with  the  nose  and  mouth  by  means  of 
the  bronchi,  trachea,  and  larynx. 

NOSE 

The  nose  is  the  special  organ  of  the  sense  of  smell,  but  it  also 
serves  as  a  passageway  for  the  entrance  of  air  to  the  respiratory 
organs.  It  consists  of  two  parts,  —  the  external  feature,  the  nose, 
and  the  internal  cavities,  the  nasal  fossae. 

The  external  nose  is  composed  of  a  triangular  framework  of 
bone  and  cartilage,  covered  by  skin  and  lined  by  mucous  membrane. 
On  its  under  surface  are  two  oval-shaped  openings  —  the  nostrils, 
which  are  the  external  openings  of  the  nasal  fossae.  The  margins 
of  the  nostrils  are  provided  with  a  number  of  stiff  hairs,  which  ar- 

247 


248 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIII 


rest  the  passage  of  dust  and  other  foreign  substances  which  might 
otherwise  be  carried  in  with  the  inspired  air. 

The  nasal  fossae  are  two  irregularly  wedge-shaped  cavities, 
separated  from  one  another  by  a  partition,  or  septum.  The 
septum  is  formed  partly  by  the  vertical  plate  of  the  ethmoid, 
partly  by  the  vomer,  and  partly  by  cartilage.  Figure  152  shows 
the  portions  formed  by  the  ethmoid,  vomer,  and  cartilage. 

The  turbinated  bones  "and  turbinated  processes  of  the  ethmoid, 
which  are  exceedingly  light  and  spongy,  project  into  the  nasal 


FRONTAL  SINUSES 
NASAL- 


VERTICAL  PLATE 
OF  ETHMOID 


CARTILAGE 
OF  SEPTUM 


MAXILLA 


SPHENOIDAL 
SINUSES 


VOMER 


FIG.  152.  —  BONKS  AND  CARTILAGE  FORMING  SEPTUM  OF  NOSE. 

cavities,  and  divide  them  into  three  incomplete  passages  from  be- 
fore backwards,  —  the  superior,  middle,  and  inferior  meatus.  The 
palate  and  maxillae  separate  the  nasal  and  mouth  cavities,  and  the 
horizontal  plate  of  the  ethmoid  forms  the  partition  between  the 
cranial  and  nasal  cavities. 

These  cavities  1  communicate  with  the  air  in  front  by  the  anterior 
nares,  or  nostrils,  while  behind  they  open  into  the  back  of  the 
pharynx  by  the  two  posterior  nares.  They  are  lined  with  mucous 
membrane 2  which  is  continuous  externally  with  the  skin,  and 
internally  with  the  mucous  membrane  lining  the  passages  and 

1  Eleven  bones  enter  into  the  formation  of  the  nasal  cavities  :  the  floor  is  formed 
by  the  palate  (2)  and  part  of  the  maxilla?  bones  (2)  ;    the  roof  is  chiefly  formed  by 
the  horizontal  plate  of  the  ethmoid  bone  (1),  the  sphenoid  (1),  and  by  the  (2)  small 
nasal  bones ;   in  the  outer  walls  we  find,  in  addition  to  processes  from  other  bones, 
the  two  scroll-like  turbinated  bones  (2).     The  vomer  (1)  forms  part  of  the  septum. 

2  It  is  known  as  the  pituitary  or  Schneiderian  membrane. 


CHAP.  XIII]  RESPIRATORY  SYSTEM 


249 


sinuses  shown  in  Fig.  97.     Inflammatory  conditions  of  the  nasal 
mucous  membrane  may  extend  into  the  sinuses. 

Advantages  of  nasal  breathing.  —  Under  normal  conditions 
breathing  should  take  place  through  the  nose  only  (1)  because  the 
arrangement  of  the  turbinated  bones  makes  the  upper  part  of  the 

SPHENOIDAI  SIN  US 


VESTIBULE 


FIG.  153.  —  SAGITTAL,  SECTION  OP  THE   FACE  AND    NECK,  SHOWING   THE    FIRST 
PORTIONS  OF  THE  ALIMENTARY  AND  RESPIRATORY  TRACTS.     (Gerrish.) 

nasal  passages  very  narrow ;  (2)  these  passages  are  thickly  lined, 
and  freely  supplied  with  blood-vessels,  so  that  they  can,  even  in  the 
very  coldest  weather,  moisten  and  warm  the  air  before  it  reaches 
the  lungs ;  and  (3)  the  presence  of  hairs  at  the  entrance  to  the 
nostrils  serves  as  filters. 

Mouth  and  pharynx.  —  The  mouth  serves  as  a  passageway  for 
the  entrance  of  air,  and  the  pharynx  transmits  the  air  from  the 
nose  or  mouth  to  the  larynx,  but  both  are  more  closely  associated 
with  digestion  than  respiration,  and  will  be  described  with  the 
digestive  organs. 


250 


ANATOMY  AND  PHYSIOLOGY    [CHAP.  XIII 


RESPIRATORY  SYSTEM 

Under  this  heading  we  group  the  organs  which  are  concerned  in 
the  process  of  respiration.  In  man  they  are  as  follows :  — 

1.  Larynx.  3.  Bronchi. 

2.  Trachea.  4.  Lungs. 

THE  LARYNX 

The  larynx,  or  organ  of  voice,  is  placed  in  the  upper  and  front 
part  of  the  neck,  between  the  base  of  the  tongue  and  the  top 

of  the  trachea. 
Above  and  behind 
lies  the  pharynx, 
which  opens  into 
the  oesophagus,  or 
gullet,  and  on 
either  side  of  it 
lie  the  great  ves- 
sels of  the  neck. 
The  larynx  is 
broad  above  and 
shaped  somewhat 
like  a  triangular 
box,  with  flat  sides 
and  prominent 
ridge  in  front.  Be- 
low it  is  narrow 
and  rounded  where 
it  blends  with  the 
trachea.  It  is  made 
up  of  nine  pieces 
of  fibro-cartilage, 
united  by  elastic 
ligaments,  and 
moved  by  numer- 
ous muscles. 

The  three  principal  cartilages  are  the  cricoid,  thyroid,  and 
epiglottis.  The  cricoid  resembles  a  seal  ring  with  the  hoop  part  in 
front  and  the  signet  part  in  the  back.  The  thyroid  resembles 


FIG.  154.  —  DIAGRAM  OF  THE  RESPIRATORY  SYSTEM. 


CHAP.  XIII]          RESPIRATORY  SYSTEM 


251 


a  shield  and  is  the  largest.  It  rests  upon  the  cricoid  and  con- 
sists of  two  square  plates,  or  alse  (right  and  left),  which  are  joined 
in  front  and  form  by  their  union  the  laryngeal  prominence, 
called  Adam's  apple.  The  epiglottis  is  shaped  like  a  leaf. 
The  stem  is  inserted  in  the  notch  between  the  two  plates  of  the 


INFERIOR 
VOCAL  FOLD 


FIG.  155.  —  LARYNX.     Viewed  from  above.     (Gerrish.) 

thyroid.  The  larynx  is  lined  throughout  by  mucous  membrane, 
which  is  continuous  above  with  that  lining  the  pharynx,  and  below 
with  that  lining  the  trachea. 

The  glottis.  —  Across  the  middle  of  the  larynx  is  a  transverse 
partition,  formed  by  two  folds  of  the  lining  mucous  membrane, 
stretching  from  side  to  side,  but  not  quite  meeting  in  the  middle 
line.  They  thus  leave  in  the  middle  line  a  chink,  or  slit,  running 
from  front  to  back,  called  the  glottis,  which  is  the  narrowest  seg- 
ment of  the  air  passages.  The  glottis  is  protected  by  the  leaf- 
shaped  lid  of  fibro-cartilage,  called  the  epiglottis,  which  shuts 
down  upon  the  opening  during  the  passage  of  food  or  other  matter 
into  the  oesophagus. 

The  vocal  cords.  —  Embedded  in  the  mucous  membrane  at  the 
edges  of  the  slit  are  fibrous  and  elastic  ligaments,  which  strengthen 
the  edges  of  the  glottis  and  give  them  elasticity.  These  ligamen- 
tous  bands,  covered  with  mucous  membrane,  are  firmly  attached 
at  either  end  to  the  cartilages  of  the  larynx,  and  are  called  the 
true  vocal  cords,  because  they  function  in  the  production  of  the 


252 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIII 


voice.  Above  the  true  vocal  cords  are  two  false  weal  cords, 
so  called  because  they  do  not  function  in  the  production  of  the 
voice. 

Variations  in  size  of  glottis.  —  The  glottis  varies  in  shape  and 
size,  according  to  the  action  of  the  muscles  upon  the  laryngeal 

walls.  When  the  larynx 
is  at  rest  during  quiet 
breathing,  the  glottis 
is  V-shaped  ;  during  a 
deep  inspiration  it  be- 
comes almost  round, 
while  during  the  pro- 
duction of  a  high  note 
the  edges  of  the  folds 
approximate  so  closely 
as  to  leave  scarcely 
any  opening  at  all. 

Voice.  —  The  vocal 
cords  produce  the 
voice.  A  blast  of  air, 
driven  by  an  expira- 
tory movement  out  of 
the  lungs,  throws  the 
two  elastic  cords  into 
vibrations.  These  im- 
part their  vibrations 
to  the  column  of  air 
above  them,  and  so 
give  rise  to  the  sound 
which  we  call  the  voice. 
The  pharynx,  mouth,  and  nasal  cavities  above  the  glottis  act  as 
resonating  cavities,  and  by  alterations  in  their  shape  and  size, 
they  are  able  to  pick  out  and  emphasize  certain  parts  of  the  tones 
produced  in  the  larynx. 

Differences  between  male  and  female  voice.  —  At  puberty  in 
the  male,  the  larynx  enlarges,  giving  rise  to  what  is  commonly 
called  Adam's  apple.  The  increase  in  the  size  of  the  larynx  causes 
an  increase  in  the  length  of  the  vocal  cords.  To  this  is  due  the 
lower  pitch  of  the  voice  in  the  male. 


FIG.  156.  —  THE  LARYNX  AS  SEEN  BY  MEANS 
or  THE  LARYNGOSCOPE  IN  DIFFERENT  CONDITIONS 
OF  THE  GLOTTIS.  A,  while  singing  a  high  note; 
B,  in  quiet  breathing  ;  C,  during  a  deep  inspiration. 
I,  base  of  tongue ;  e,  upper  free  edge  of  epiglottis ; 
e',  cushion  of  the  epiglottis ;  ph,  part  of  anterior 
wall  of  pharynx ;  cv,  the  true  vocal  folds ;  cvs,  the 
false  vocal  folds ;  tr,  the  trachea  with  its  rings. 


CHAP.  XIII]  RESPIRATORY  SYSTEM 


253 


THE  TRACHEA 

The  trachea,   or  windpipe,   is  a  fibrous  and  muscular  tube, 
about  four  and  a  half  inches  (11.2  cm.)  in  length,  and  three-quar- 


Superior 
Horn 


Inferior 
Horn 


FIG.  157.  —  FRONT  VIEW  OF  CARTILAGES  OF  LARYNX.     Trachea  and  Bronchi. 

ters  of  an  inch  (1.9  cm.)  from  side  to  side.  It  lies  in  front  of  the 
oesophagus  and  extends  from  the  larynx  on  the  level  of  the  sixth 
cervical  vertebra,  to  opposite  the  fourth  or  fifth  thoracic  vertebra, 


254  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIII 

where  it  divides  into  two  tubes,  —  the  two  bronchi,  —  one  for  each 
lung. 

The  walls  are  strengthened  and  rendered  more  rigid  by  hoops 
of  cartilage  embedded  in  the  fibrous  tissue.  These  hoops  are 
C-shaped  and  incomplete  behind,  the  cartilaginous  rings  being 
completed  by  bands  of  plain  muscular  tissue  where  the  trachea 
comes  in  contact  with  the  oesophagus.  Like  the  larynx,  it  is 
lined  by  mucous  membrane,  and  has  a  ciliated  epithelium  upon 
its  inner  surface.  The  mucous  membrane,  which  also  extends 
into  the  bronchial  tubes,  keeps  the  internal  surface  of  the  air- 
passages  free  from  impurities;  the  sticky  mucus  entangles  par- 
ticles of  dust  and  other  matters  breathed  in  with  the  air,  and  the 
incessant  movements  of  the  cilia  continually  sweep  this  dirt- 
laden  mucus  upward  and  outward. 

THE   BRONCHI 

The  two  bronchi,  into  which  the  trachea  divides,  differ  slightly; 
the  right  bronchus  is  shorter,  wider,  and  more  nearly  horizontal, 
the  left  bronchus  is  longer,  narrower,  and  more  nearly  vertical. 
They  enter  the  right  and  left  lung,  respectively,  and  then  break  up 
into  a  great  number  of  smaller  branches  which  are  called  the  bron- 
chial tubes,  or  bronchioles.  The  two  bronchi  resemble  the  trachea 
in  structure;  but  as  the  bronchial  tubes  divide  and  subdivide 
their  walls  become  thinner,  the  small  plates  of  cartilage  cease, 
the  fibrous  tissue  disappears,  and  the  finer  tubes  are  composed 
of  only  a  thin  layer  of  muscular  and  elastic  tissue  lined  by  mucous 
membrane. 

LUNGS 

The  lungs  are  cone-shaped  organs  which  occupy  almost  all  of 
the  cavity  of  the  thorax  that  is  not  taken  up  by  the  heart,  the  large 
blood-vessels,  the  lymphatics,  and  the  oesophagus.  Each  lung 
presents  an  outer  surface  which  is  convex,  a  base  which  is  concave 
to  fit  over  the  convex  portion  of  the  diaphragm,  and  a  summit  or 
apex  which  rises  half  an  inch  above  the  clavicle.  On  the  inner 
surface  is  a  vertical  notch  called  the  hilum,  which  gives  passage 
to  the  bronchi,  blood-vessels,  lymph-vessels,  and  nerves. 

The  right  lung  is  the  larger  and  heavier ;  it  is  broader  than  the 
left,  owing  to  the  inclination  of  the  heart  to  the  left  side;  it  is 


CHAP.  XIII] 


RESPIRATORY  SYSTEM 


255 


also  shorter  by  one  inch,  in  consequence  of  the  diaphragm  rising 
higher  on  the  right  side  to  accommodate  the  liver.  The  right 
lung  is  divided  by  fissures  into  three  lobes,  upper,  middle,  and 
lower. 

The  left  lung  is  smaller,  narrower,  and  longer  than  the  right. 
It  is  divided  into  two  lobes,  upper  and  lower.  The  front 
border  is  deeply  notched  to  accommodate  the  heart. 


RIGHT  LUNG 


LEFT  LUNG 


FlG. 


158.  —  BRONCHI   AND    BRONCHIOLES.     The  lungs  have  been   widely   sepa- 
rated and  tissue  cut  away  to  expose  the  air-tubes.     (Gerrish.) 


Anatomy  of  the  lungs.  —  The  lungs  are  hollow,  rather  spongy 
organs,  and  consist  of  the  bronchial  tubes  and  their  terminal 
dilatations,  numerous  blood-vessels,  lymphatics,  nerves,  and  an 
abundance  of  fine,  elastic  connective  tissue,  binding  all  together. 
(See  Fig.  107.)  Each  lobe  of  the  lung  is  composed  of  many  lobules, 
and  into  each  lobule  a  bronchiole  enters  and  terminates  in  an  en- 
largement having  more  or  less  the  shape  of  a  funnel,  and  called  an 
infundibulum.  From  each  infundibulum  there  is  a  series  of  small 
sac-like  projections  known  as  alveoli,  the  walls  of  which  are  honey- 
combed with  cavities  called  the  air-cells.  In  this  way  the  amount 


FIG.  159.  —  DIAGRAM  OF  A  LOBULE  OF  THE  LUNG.  A  bronchiole  is  seen  divid- 
ing into  two  branches,  one  of  which  runs  upward  and  ends  in  the  lobule.  In  the 
lobule  are  four  groups  of  infundibula.  At  the  left  are  two  infundibula,  the  alveoli 
of  which  present  their  outer  surfaces.  Next  are  three  infundibula  in  vertical 
section,  the  alveoli  of  each  opening  into  the  common  passageway.  In  the  next 
group  the  first  infundibulum  shows  a  pulmonary  arteriole  surrounding  the  opening 
of  each  alveolus,  and  the  second  gives  the  same  with  the  addition  of  the  close 
capillary  network  in  the  wall  of  each  alveolus.  Around  the  fourth  group  is  a  deep 
deposit  of  pigment,  such  as  occurs  in  old  age,  and  in  the  lungs  of  those  who  inhale 
coal  dust  and  the  like.  On  the  bronchiole  lies  a  1  (ranch  of  the  pulmonary  artery 
(blue),  bringing  blood  to  the  infundibula  for  aeration.  Beginning  between  the 
infundibula  are  the  radicles  of  the  pulmonary  vein  (red),  a  root  of  which  lies  upon 
the  bronchiole.  The  bronchial  artery  is  shown  as  a  small  vessel  bringing  nutrient 
blood  to  the  bronchiole.  (Gerrish.) 

256 


CHAP.  XIII]  RESPIRATORY  SYSTEM  257 

of  surface  exposed  to  the  air  and  covered  by  the  capillaries  is  so 
immensely  increased  that  it  is  estimated  the  entire  inner  surface 
of  the  lungs  is  one  hundred  times  greater  than  the  skin  surface  of 
the  body.1 

Blood-vessels  of  the  lungs.  —  Two  sets  of  vessels  are  distrib- 
uted to  the  lungs :  (1)  the  branches  of  the  pulmonary  artery, 
and  (2)  the  branches  of  the  bronchial  arteries. 

(1)  The   branches   of  the   pulmonary   artery   accompany   the 
bronchial  tubes  and  form  a  plexus  of  capillaries  around  the  al- 
veoli.    The  walls  of  the  bronchioles  consist  of  a  single  layer  of 
flattened  epithelioid  cells,  surrounded  by  a  fine,  elastic  connec- 
tive tissue,  and  are  exceedingly  thin  and  delicate.     Immediately 
beneath  the  layer  of  flat  cells,  and  lodged  in  the  elastic  connective 
tissue,  is  this  very  close  plexus  of  capillary  blood-vessels ;  and  the 
air  reaching  the  alveoli  by  the  bronchial  tubes  is  separated  from 
the  blood  in  the  capillaries  only  by  the  thin  membranes  forming 
their  respective  walls.     The  pulmonary  veins  begin  at  the  margin 
of  the  alveoli  and  return  the  blood  distributed  by  the  pulmonary 
artery. 

(2)  The  branches  of  the  bronchial  arteries  supply  blood  to  the 
lung  substance,  —  the  bronchial  tubes,  coats  of  the  blood-vessels, 
the  lymph  nodes,  and  the  pleura.      The  bronchial  veins  return 
the  blood  distributed  by  the  bronchial  arteries. 

Pleura.  —  Each  lung  is  enclosed  in  a  serous  sac,  the  pleura, 
one.  layer  of  which  is  closely  adherent  to  the  walls  of  the  chest  and 
diaphragm  (parietal) ;  the  other  closely  covers  the  lung  (visceral). 
The  two  layers  of  the  pleural  sacs,  moistened  by  serum,  are  nor- 
mally in  close  contact ;  they  move  easily  upon  one  another,  and 
prevent  the  friction  that  would  otherwise  occur  between  the 
lungs  and  the  walls  of  the  chest  with  every  respiration.  Inflam- 
mation of  the  pleura  is  called  pleurisy. 

Mediastinum.  —  The  mediastinum  is  the  space  left  in  the  median 
portion  of  the  thorax  between  the  pleural  sacs.  It  extends  from 
the  sternum  to  the  spinal  column,  and  contains  a  portion  of  many 
organs,  i.e.,  the  trachea,  oesophagus,  great  vessels  connected  with 
the  heart,  lymph-nodes,  thoracic  duct,  and  various  nerves. 

1  It  is  estimated  that  the  amount  of  lung  surface  which  is  exposed  to  the  air  is 
90  square  metres  and  the  average  skin  surface  is  estimated  to  be  &  of  one  square 
metre. 


258  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIII 

RESPIRATION 

The  main  purpose  of  respiration  is  to  supply  all  the  cells  of  the 
body  with  oxygen  and  rid  them  of  the  excess  carbon  dioxide  which 
results  from  oxidation.  It  also  helps  to  equalize  the  temperature 
of  the  body  and  get  rid  of  excess  water.  To  accomplish  these 
purposes  three  processes  are  necessary  :  — 

(1)  Breathing.  —  The  process  of  breathing  may  be  subdivided 
into  inspiration  or  breathing  in,  and  expiration  or  breathing  out. 
Inspiration  is  a  preliminary  process  whereby  air  is  introduced  into 
the  lungs.     Expiration  is  the  process  by  which  air  is  expelled  from 
the  lungs.     This  air  has  given  up  about  one-fourth  of  its  oxygen 
and  increased  the  quantity  of  carbon  dioxide  one  hundred  times. 
(See  page  263.) 

(2)  External  respiration.  —  This  includes  two  processes :    (a) 
external  oxygen  supply  or  the  passage  of  oxygen  from  the  alveoli 
of  the  lungs  to  the  blood  ;  and  (6)  external  carbon  dioxide  elimi- 
nation or  the  passage  of  carbon  dioxide  from  the  blood  into  the 
alveoli  of  the  lungs. 

(3)  Internal  respiration.  —  This   also   includes   two  processes : 
(a)  internal  oxygen  supply  or  the  passage  of  oxygen  from  the 
blood  to  the  cells  of  the  tissues ;   and  (6)  internal  carbon  dioxide 
elimination  or  the  passage  of  carbon  dioxide  from  the  cells  of  the 
tissues  to  the  blood. 

It  is  evident  that  external  respiration  is  a  process  that  takes 
place  in  the  lungs  and  that  internal  respiration  is  a  process  that 
takes  place  in  all  the  cells  that  make  up  the  tissues  of  the  body. 

Mechanism  of  inspiration  and  expiration.  —  During  inspiration 
the  cavity  of  the  chest  is  enlarged  in  all  three  diameters:  (1) 
antero-posterior,  (2)  lateral,  and  (3)  vertical.  This  is  brought 
about  by  the  action  of  the  intercostal  and  other  muscles,  which 
elevate  the  ribs  and  thereby  increase  the  antero-posterior  and 
lateral  diameters.  The  descent  of  the  diaphragm  increases  the 
vertical  diameter.  The  lungs  are  expanded  exactly  in  proportion 
as  the  cavity  enlarges.  The  expansion  affects  chiefly  the  elastic 
sacs  or  alveoli,  and  air  presses  into  them  as  into  a  widening  bellows. 
The  atmospheric  pressure  outside  the  body  is  greater  than  the 
pressure  within  the  alveoli,  and  this  forces  the  air  in.  Upon  the 
relaxation  of  the  inspiratory  muscles,  the  elasticity  of  the  lungs, 


CHAP.  XIII]          RESPIRATORY  SYSTEM  259 

and  the  weight  and  elasticity  of  the  chest  walls,  cause  the  chest  to 
return  to  its  original  size,  in  consequence  of  which  the  air  is  ex- 
pelled from  the  lungs.  As  in  the  heart,  the  auricular  systole,  the 
ventricular  systole,  and  then  a  pause,  follow  in  regular  order ;  so  in 
the  lungs  the  inspiration,  the  expiration,  and  then  a  pause,  succeed 
one  another. 

Control  of  respiration.  —  Respiration  is  both  a  voluntary  and 
an  involuntary  act.  It  is  possible  for  a  short  time  to  increase  or 
decrease  the  rate  of  respiration  within  certain  limits  by  voluntary 
effort,  but  this  cannot  be  done  continuously.  If  we  intentionally 
arrest  the  breathing  or  diminish  its  frequency,  after  a  short  time 
the  nervous  impulse  becomes  too  strong  to  be  controlled,  and  the 
movements  will  recommence,  as  usual.  If,  on  the  other  hand,  we 
purposely  accelerate  respiration  to  any  great  degree,  the  exertion 
soon  becomes  too  fatiguing  for  continuance,  and  the  movements 
return  to  their  normal  standard. 

Cause  of  respiration.  —  Unlike  the  beat  of  the  heart  the  con- 
tractions of  the  respiratory  muscles  are  entirely  dependent  on  the 
nervous  system,  especially  that  part  known  as  the  respiratory 
centre,  which  is  located  in  the  medulla  oblongata.1  Efferent  nerves 
from  the  respiratory  centre  travel  down  the  spinal  cord  and  end 
at  different  levels,  where  they  connect  with  the  fibres  of  the 
vagi  and  sympathetic  nerves  that  are  distributed  in  the  lung 
tissue.  Afferent  nerves  lead  from  these  different  levels  to  the 
respiratory  centre. 

The  consensus  of  opinion  at  the  present  time  seems  to  be  that 
the  action  of  the  respiratory  centre  is  automatic,  but  that  the 
rate  and  rhythm  of  the  respiratory  movements  are  controlled 
(1)  by  the  vagi  nerves,  and  (2)  by  the  chemical  condition  of 
the  blood. 

(1)  The  fibres  from  the  vagi  are  of  two  kinds :    (a)  inspiratory 
fibres  which  tend  to  increase  the  rate  of  respiration,  and  (6)  ex- 
piratory fibres  which  check  the  action  of  the  inspiratory  set.     The 
inspiratory  fibres  are  stimulated  to  action  when  the  lung  collapses ; 
the  expiratory  when  the  lung  expands. 

(2)  The  respiratory  centre  shows  a  specific  irritability  for  carbon 

1  It  is  important  to  remember  the  difference  between  the  heart  action  and 
respiration :  the  heart  beats  of  itself,  and  the  respiratory  muscles  are  thrown  into 
contraction  by  the  brain. 


260  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XIII 

dioxide,  and  an  increased  amount  of  carbon  dioxide  in  the  blood  acts 
as  a  stimulus,  increasing  the  rate  and  depth  of  the  respirations,  so 
that  the  lungs  are  more  thoroughly  ventilated.  Increased  activ- 
ity, or  any  abnormal  condition  that  increases  the  oxf  Nation  of  the 
tissues,  naturally  results  in  an  increased  production  of  carbon 
dioxide,  and  an  increase  in  the  rate  and  depth  of  the  respirations. 
On  the  other  hand,  an  excess  of  oxygen  in  the  blood  may  cause  a 
condition  known  as  physiological  apnoea,  i.e.,  where  the  blood  is 
so  rich  in  oxygen  and  poor  in  carbon  dioxide  that  a  respiratory 
act  is  unnecessary. 

Reflex  stimulation  of  the  respiratory  centre.  —  Every  one  must 
have  noticed  that  the  respiratory  movements  are  affected  by 
stimulation  of  the  sensory  nerves.  Strong  emotion,  sudden  pain, 
or  a  dash  of  cold  water  on  the  skin  produce  changes  in  the  rate  of 
the  respirations.  It  is  assumed,  therefore,  that  the  respiratory 
centre  is  in  connection  with  the  sensory  fibres  of  all  the  cranial 
and  spinal  nerves. 

Cause  of  the  first  respiration.  —  The  immediate  cause  of  the 
first  respiratory  effort  is  closely  connected  with  the  cause  of  the 
activity  of  the  respiratory  centre  during  life.  The  stimulus  is 
supposed  to  come  from  (1)  the  increased  amount  of  carbon  dioxide 
in  the  blood,  due  to  the  cutting  of  the  umbilical  cord ;  and  (2) 
stimulation  of  the  sensory  nerves  of  the  skin,  due  to  cooler  air, 
handling,  etc.  During  intrauterine  life  the  foetus  receives  its 
supply  of  oxygen,  and  gives  off  carbon  dioxide  by  means  of  the 
blood-vessels  of  the  cord,  which  connect  with  the  placenta.  The 
lungs  are  in  a  collapsed  condition  and  contain  no  air.  The  walls 
of  the  air-sacs  are  in  close  contact,  and  the  walls  of  the  smaller 
bronchial  tubes,  or  bronchioles,  touch  one  another.  When  the 
chest  expands  with  the  first  breath,  the  inspired  air  has  to 
overcome  the  adhesions  existing  between  the  walls  of  the  bron- 
chioles and  air-sacs.  The  force  of  this  first  inspiratory  effort, 
spent  in  opening  out  and  unfolding,  as  it  were,  the  inner  recesses 
of  the  lungs,  is  considerable.  In  the  succeeding  expiration,  most  of 
the  air  introduced  by  the  first  inspiration  remains  in  the  lungs, 
succeeding  breaths  unfold  the  lungs  more  and  more,  until  finally 
the  air-sacs  and  bronchioles  are  all  opened  up  and  filled  with 
air.  The  lungs  thus  once  filled  with  air  are  never  completely 
emptied  again  until  after  death. 


CHAP.  XIII]          RESPIRATORY  SYSTEM  261 

Frequency  of  respiration.  —  The  average  rate  of  respiration  for 
an  adult  is  about  eighteen  per  minute.  Even  in  health  this  rate 
may  be  increased  by  muscular  exercise,  emotion,  etc.  Anything 
that  affects  the  heart-beat  will  have  a  similar  effect  on  the  respira- 
tions and  except  in  diseased  conditions  the  ratio  of  the  respirations 
and  heart-beat  (1  to  4)  remains  the  same.  Age  has  a  marked  in- 
fluence. The  average  rate  in  the  newly  born  infant  has  been  found 
to  be  forty-four  per  minute,  and  at  the  age  of  five  years,  twenty- 
six  per  minute.  It  is  reduced  between  the  ages  of  fifteen  and 
twenty  to  the  normal  standard. 

Respiratory  sounds.  —  The  entry  and  exit  of  the  air  are  ac- 
companied by  respiratory  sounds  or  murmurs.  These  murmurs 
differ  as  the  air  passes  through  the  trachea,  the  larger  bronchial 
tubes,  and  the  bronchioles.  They  are  variously  modified  in  lung 
disease,  and  are  then  often  spoken  of  under  the  name  of  rales. 
In  labored  breathing  the  contraction  of  the  respiratory  muscles 
not  usually  brought  into  play,  such  as  the  muscles  of  the  throat 
and  nostrils,  becomes  very  marked. 

Effects  of  respiration  upon  the  blood.  —  Once  or  twice  each 
minute  all  the  blood  in  the  body  passes  through  the  capillaries  of 
the  lungs.  This  means  that  the  time  during  which  any  portion 
of  blood  is  in  a  position  for  respiratory  exchange  is  only  a  second 
or  two.  Yet  during  this  time,  the  following  changes  take  place : 
(1)  it  loses  carbon  dioxide;  (2)  it  gains  oxygen,  which  combines 
with  the  reduced  haemoglobin  of  the  red  cells  and  turns  it  into 
oxyhsemoglobin,  and  as  a  result  of  this  the  crimson  color  shifts  to 
scarlet ;  and  (3)  the  temperature  is  slightly  reduced. 

It  is  helpful  to  compare  the  amounts  of  oxygen  and  carbon 
dioxide  found  in  the  venous  blood  brought  to  the  lungs,  and  the 
amounts  found  in  the  arterial  blood  carried  from  the  lungs. 


OXYGEN 

CARBON  DIOXIDE 

NITROGEN 

Venous  blood  contains    .... 
Arterial  blood  contains   .... 

8-12% 
20% 

45-50% 

38% 

1-2% 

1-2% 

From  these  figures  it  is  evident  that  the  cells  do  not  remove  all 
the  oxygen  nor  do  the  lungs  remove  all  the  carbon  dioxide  from  the 
circulating  blood.  There  is  always  a  considerable  amount  of 


262  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIII 

oxygen  in  venous  blood,  also  a  considerable  amount  of  carbon 
dioxide  in  arterial  blood.  Consequently,  the  main  result  of  the 
respiratory  exchange  is  to  keep  the  gas  content  of  the  arterial  blood 
nearly  constant  at  the  figures  given.  Under  normal  conditions 
it  is  not  possible  to  increase  appreciably  the  amount  of  oxygen 
absorbed  by  the  blood  flowing  through  the  lungs.1 

Capacity  of  the  lungs.  —  As  the  lungs  are  not  emptied  at  each 
expiration,  neither  are  they  filled.  If  filled  to  their  utmost,  they 
can  hold  a  little  more  than  one  gallon  (4500  c.c.)  of  air.  This  total 
is  divided  as  follows :  — 

(1)  Tidal.  (3)  Reserve. 

(2)  Complemental.  (4)  Residual. 

Tidal  air  is  the  air  introduced  with  every  ordinary  inspiration 
(30  cu.  in.  or  about  500  c.c.). 

Complemental  air  is  the  excess  over  the  tidal  air  which  may 
be  introduced  during  a  forced  inspiration. 

Reserve  air  is  the  amount  of  air  in  addition  to  the  tidal  air 
one  can  expel  from  the  lungs  in  a  forced  expiration. 

Residual  air  is  the  air  remaining  in  the  lungs  after  the  most 
powerful  expiration. 

The  vital  capacity  is  the  sum  of  the  tidal,  Complemental,  and 
reserve  air  added  together.  It  equals  about  225  cubic  inches 
(3700  c.c.). 

It  is  not  correct  to  think  of  the  residual  air  in  the  lungs  as 
stationary,  for  the  air  is  being  constantly  moved  and  renewed. 
This  movement  is  maintained  by  :  (1)  the  alternate  expansion  and 
collapse  of  the  lungs  in  respiration,  (2)  the  convection  2  currents 
due  to  the  differences  in  temperature  between  the  inspired  air  and 
the  residual  air,  (3)  the  pulsation  of  the  arteries,  and  (4)  the 
difference  in  the  proportion  of  carbon  dioxide  and  oxygen  in  the 
inspired  air  and  residual  air.  This  fourth  factor  is  also  responsible 
for  the  interchange  of  gases  between  the  air  in  the  air-sacs  and  the 

1  Student  nurses  sometimes  find  it  difficult  to  reconcile  this  fact  with  the  practice 
of  using  pure  oxygen  in  critical  cases  of  pulmonary  disease.      The  relief  of  the 
pneumonia  patient  who  inhales  pure  oxygen  is  usually  marked  because  the  blood 
absorbs  an  increased  amount  of  oxygen.     The  reason  for  this  seeming  contradiction 
is  that  normal  blood  cannot  absorb  an  increased  amount  of  oxygen,  but  in  the  case 
of  the  pneumonia  patient  the  composition  of  the  blood  as  regards  oxygen  is  below 
normal,  and  the  inhalation  of  pure  oxygen  brings  it  up  to  the  standard,  hence  the 
marked  relief. 

2  See  Glossary,  p.  494. 


CHAP.  XIII]          RESPIRATORY  SYSTEM 


263 


blood  in  the  capillaries.  The  reason  is  that  the  blood  contains 
more  carbon  dioxide  and  less  oxygen  than  the  air  in  the  alveoli, 
and  the  tendency  of  gases  is  always  to  mix  in  uniform  proportions. 
The  effects  of  respiration  upon  the  air  outside  the  body.  —  With 
every  inspiration  a  well-grown  man  takes  into  his  lungs  about 
30  cubic  inches  (500  c.c.)  of  air.  The  air  he  takes  in  differs  from 
the  air  he  gives  out  mainly  in  three  particulars :  — 

1.  Whatever  the  temperature  of  the  external  air,  the  expired 
air  is  nearly  as  hot  as  the  blood ;  namely,  of  a  temperature  between 
98°  and  100°  F.  (36.7°  and  37.8°  C.). 

2.  However  dry  the  external  air  may  be,  the  expired  air  is 
quite,  or  nearly,  saturated  with  moisture. 

3.  When  breathed  the  air  loses  4.94  per  cent  of  oxygen  and 
gains  4.38  per  cent  of  carbon  dioxide.     Thus :  - 


OXYGEN 

CARBON  DIOXIDE 

NITROGEN 

Inspired  air       

2096% 

004% 

79% 

Expired  air        

1602% 

438% 

79% 

4.94  loss 

4.34  gain 

0 

Ventilation.  —  Since  at  every  breath  the  external  air  gains 
carbon  dioxide  and  loses  oxygen,  it  was  formerly  taught  that  the 
general  discomfort,  headache,  and  languor  that  result  from  sitting 
in  a  badly  ventilated  room  were  due  to  the  increase  in  carbon  di- 
oxide and  the  loss  of  oxygen.  The  results  of  many  experiments 
seem  to  prove  that  people  can  become  so  accustomed  to  a  high 
percentage  of  carbon  dioxide  and  a  low  percentage  of  oxygen 
that  they  suffer  little  discomfort ;  though  odors  given  off  from  the 
body  and  its  clothing  when  present  in  any  amount  may  affect  the 
nervous  system  disagreeably.  It  is  now  thought  that  the  injurious 
effects  of  remaining  in  a  badly  ventilated  room  are  due  to  inter- 
ference with  the  heat-regulating  mechanism  of  the  body.  Under 
favorable  conditions  the  surface  of  the  human  body  is  kept  com- 
fortably cool  by  the  air  currents  which  pass  over  it  and  by  the 
evaporation  of  perspiration.  The  former  are  an  aid  to  the  latter. 
In  a  confined  space  there  is  a  lack  of  movement  in  the  air  and  it 
tends  to  become  warm  and  humid.  Moisture  is  not  taken  from 
the  skin  promptly  and  the  temperature  rises.  This  results  in  a 


264  ANATOMY  AND  PHYSIOLOGY    [CHAP.  XIII 

dilatation  of  the  blood-vessels  of  the  skin  and  an  increased  amount 
of  blood  is  sent  to  the  surface  of  the  body,  thereby  increasing  the 
unpleasant  warmth.  There  is  likely  to  be  some  reduction  of  the 
general  blood-pressure  leading  to  drowsiness  or  at  least  a  feeling 
of  inertia.  In  accordance  with  these  views,  the  most  effective 
precautions  that  can  be  taken  to  secure  comfort  in  a  room 
are  to  keep  it  cool  and  to  have  some  circulation  of  the  air.  It 
has  been  shown  that  starting  an  electric  fan  in  a  close  room  may 
relieve  an  almost  intolerable  condition.  It  does  not  improve  the 
air  chemically  but  it  favors  the  removal  of  heat  from  the  bodies  of 
the  inmates  and  braces  up  their  vasomotor  systems.  One  writer 
suggests  that  the  real  difficulty  with  a  stuffy  room  is  that  there  is 
a  lack  of  stimulation  for  the  nervous  system.  One  becomes  re- 
laxed and  indolent  because  the  nerve-endings  in  the  skin  are  not 
being  played  upon  as  they  would  be  by  a  constant  change  in  en- 
vironmental conditions.  Because  of  these  facts  we  are  now  taught 
that  proper  ventilation  requires  (1)  there  must  be  continuous  move- 
ment of  the  air ;  (2)  the  temperature  and  degree  of  humidity  must 
favor  the  evaporation  of  perspiration  from  the  skin;  (3)  odors 
from  skin,  clothing,  light,  and  other  sources  must  be  eliminated. 

Dyspnoea.  —  The  word  dyspnoea  means  difficult  breathing. 
It  is  caused  by  (1)  an  increase  in  the  percentage  of  carbon  dioxide 
in  the  blood,  (2)  a  decrease  in  the  oxygen,  and  (3)  any  con- 
dition that  stimulates  the  sensory  nerves  and  causes  pain  in  the 
lungs. 

Hyperpncea.  —  The  word  hyperpncea  means  excessive  breath- 
ing and  is  applied  to  the  initial  stages  of  dyspnoea,  when  the  res- 
pirations are  simply  increased. 

Apncea.  —  The  word  apnoea  means  a  lack  of  breathing. 

Cheyne-Stokes  respirations.  —  This  is  a  type  of  respirations 
which  was  first  described  by  the  two  physicians  whose  names  it 
bears.  It  appears  in  two  forms :  (1)  the  respirations  increase  in 
force  and  frequency  up  to  a  certain  point,  and  then  gradually  de- 
crease until  they  cease  altogether,  and  there  is  a  short  period  of 
apncea,  then  the  respirations  recommence  and  the  cycle  is  repeated. 
(2)  The  respirations  increase  in  force  and  frequency  up  to  a  certain 
point,  then  cease,  and  the  period  of  apncea  intervenes,  without 
the  gradual  cessation  of  the  respirations.  This  condition  is  asso- 
ciated with  disease  of  the  kidney,  brain,  or  heart.  The  cause  is 


CHAP.  XIII]          RESPIRATORY  SYSTEM  265 

not  settled,  but  it  is  of  bad  prognosis  and  generally  indicates  a 
fatal  termination. 

(Edematous  respiration.  —  When  the  air  cells  become  infil- 
trated with  fluid  from  the  blood,  the  breathing  becomes  oedema- 
tous  and  is  recognized  by  the  moist,  rattling  sounds,  called  rales, 
that  accompany  each  inspiration.  It  is  a  serious  condition  be- 


FIG.  160.  —  STETHOGRAPH  TRACING  OF  CHEYNE-STOKES  RESPIRATIONS  IN  A 
MAN.     The  time  is  marked  in  seconds.     (Halliburton.) 

cause  it  interferes  with  aeration  of  the  blood  and  often  results  in 
asphyxia. 

Asphyxia.  —  This  condition  is  usually  the  sequel  to  severe  dysp- 
noea and  cedematous  respiration.  It  is  produced  by  any  condition 
that  causes  prolonged  interference  with  the  aeration  of  the  blood. 
After  death  from  asphyxia  it  will  be  found  that  the  right  side  of 
the  heart,  the  pulmonary  arteries,  and  the  systemic  veins  are  over- 
loaded, and  the  left  side  of  the  heart,  the  pulmonary  veins,  and  the 
systemic  arteries  are  empty. 

MODIFIED   RESPIRATORY  MOVEMENTS 

Various  emotions  may  be  expressed  by  means  of  the  respiratory 
apparatus. 

Sighing  is  a  deep  and  long-drawn  inspiration,  followed  by   a 
sudden  expiration. 

Yawning  is  an  inspiration,  deeper  and  longer  continued  than  a 
sigh,  drawn  through  the  widely  open  mouth,  and  accompanied 
by  a  peculiar  depression  of  the  lower  jaw. 

Hiccough  is  caused  by  a  sudden  inspiratory  contraction  of  the 
diaphragm ;  the  glottis  suddenly  closes  and  cuts  off  the  column 
of  air  just  entering,  which,  striking  upon  the  closed  glottis,  gives 
rise  to  the  characteristic  sound. 


266  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIII 

Sobbing  is  a  series  of  convulsive  inspirations  during  which  the 
glottis  is  closed,  so  that  little  or  no  air  enters  the  chest. 

Coughing  consists,  in  the  first  place,  of  a  deep  and  long-drawn 
inspiration  by  which  the  lungs  are  well  filled  with  air.  This 
is  followed  by  a  complete  closure  of  the  glottis,  and  then  comes 
a  forcible  and  sudden  expiration,  in  the  midst  of  which  the  glottis 
suddenly  opens,  and  thus  a  blast  of  air  is  driven  through  the  upper 
respiratory  passages. 

Sneezing  consists  of  a  deep  inspiration,  followed  by  a  sudden 
and  forced  expiration,  which  directs  the  air  through  the  nasal 
passages. 

Laughing  consists  essentially  in  an  inspiration,  followed  by 
a  whole  series  of  short,  spasmodic  expirations,  the  glottis  being 
freely  open  during  the  whole  time,  and  the  vocal  cords  being 
thrown  into  characteristic  vibrations. 

Crying  consists  of  the  same  respiratory  movements  as  laugh- 
ing; the  rhythm  and  the  accompanying  facial  expressions  are, 
however,  different,  though  laughing  and  crying  often  become 
indistinguishable. 

Speaking  consists  of  a  voluntary  expiration  and  the  vibration 
of  the  vocal  cords  as  the  air  passes  over  them. 


CHAP.  XIII] 


SUMMARY 


267 


SUMMARY 

Respiration  is  dependent  upon  the  proper  functioning  of  organs  that  com- 
prise the  respiratory  system.  Air  passes  through  the  nose  or  mouth  to 
these  organs. 

Special  organ  of  the  sense  of  smell. 
Function          j  Passageway  for  entrance  of  air  to  the 

respiratory  organs. 

Framework  of  bone  (nasal)  and  cartilage. 
Covered  with  skin,  lined  with  mucous 
External  I      membrane    known    as    pituitary,    or 

nose  Schneiderian. 

Nostrils    are    oval-shaped    openings   on 
under  surface,  separated  by  a  partition. 
Extend  from  nostrils  to  the  pharynx. 
Two  wedge-shaped  cavities. 
2  palate. 
2  maxillae. 
1  ethmoid. 

1  sphenoid. 

2  nasal. 

2  turbinated, 
and  pro- 
cesses of 
the  eth- 
moid 


Nose 


Respiratory 
System 


Larynx 


Internal 
cavities,  or 
nasal  fossae 


Formed  by 


Superior 

meatus. 
Middle 

meatus. 
Inferior 

meatus. 
J_  vomer. 
%  11  bones. 

Advantages  Warmed, 

of  nasal  Air  Moistened 

breathing  Filtered. 

1.  Frontal. 
Communicat-      2.  Ethmoidal. 
ing  sinuses     3.  Maxillary  or  antrums  of  Highmore. 
(  4.  Sphenoidal. 

1.  Larynx.  3.  Bronchi. 

2.  Trachea.  4.  Lungs. 
Special  organ  of  voice. 

Triangular  box  made  up  of  nine  pieces  of  cartilage. 

Situated  between  the  tongue  and  trachea. 

Contains  vocal  cords. 

Slit  or  opening  between  cords  called  glottis,  which  is  pro- 
tected by  leaf -shaped  lid  called  epiglottis. 

Connected  with  external  i  Mouth, 
air  by  \  Nose. 


268 


ANATOMY  AND  PHYSIOLOGY    [CHAP.  XIH 


Voice 


Trachea 


Bronchi 


Lungs 


Right 


Left 


Produced  by  vibrations  of  vocal  cords. 

Pharynx. 
Resonating  cavities  Mouth. 

Nasal  cavities. 
Lower  pitch  of  male  voice  is  due  to  greater  length  of  vocal 

cords. 

Fibrous  and  muscular  tube,  4|  in.  long. 
Strengthened  by  C-shaped  J  Complete  in  front. 

hoops  of  cartilage  1  Incomplete  behind. 

In  front  of  oesophagus. 
Extends  from  larynx  to  fifth  thoracic  vertebra,  where  it 

divides  into  two  bronchi. 
Right  and  left  —  structure  similar  to  trachea. 

1  in.  long. 
Almost  horizontal. 

2  in.  long. 
Almost  vertical. 

Divide  into  innumerable  bronchial  tubes  or  bronchioles. 
Location  —  Occupy  all  of  the  cavity  of  the  thorax  that  is 
not  taken  up  by  the  heart,  blood-vessels,  lymphatics, 
oesophagus,  and  lymph  nodes. 

Outer  surface  convex  to  fit  in  concave 

cavity. 

Base   concave    to  fit   over  convex  dia- 
phragm. 

Apex  rises  half  an  inch  above  the  clavicle. 
Hilum   or   depression   on   inner   surface 
gives  passage  to  bronchi,  blood-vessels, 
lymphatics,  and  nerves. 
Larger,  heavier,  broader,  shorter  —  three 

lobes. 
Smaller,  narrower,  longer,  front  border 

deeply  indented  —  two  lobes. 
Hollow,  spongy  organs.  Consist  of  bron- 
chial tubes  —  infundibula  —  alveoli, 
also  blood-vessels,  lymphatics,  and 
nerves  held  together  by  connective 
tissues. 

Blood  for  aeration. 
Accompanies  bronchial  tubes. 
Pulmonary    Plexus  of  capillaries  around 
artery  alveoli. 

Returned     by     pulmonary 

veins, 
arteries  —  supply    lung   sub- 


Cone-shaped 
organs 


Right 


Left 


Anatomy 


Blood-vessels 


Nerves 


Bronchial 

stance. 

1 .  Branches  from  the  sympathetic  system, 

2.  Branches  from  the  vagi. 


CHAP.  XIII] 


SUMMARY 


269 


Moistened 
by  serum. 


Function 


Respiration 


Closed  sac.     Envelops  lungs,  but  they  are  not  in  it. 

Visceral  —  next  to  lung 

Pleura    .     .      {  Two  layers          Parietal  —  outside  of  vis- 
ceral 

Function  —  To  lessen  friction. 
Mediastinum  —  Space  between  pleural  sacs.     Extends  from  sternum  to 
spinal  column. 

f  Increase  the  amount  of  oxygen. 

J  Decrease  the  amount  of  carbon  dioxide. 

]  Help  to  maintain  temperature. 

[  Help  to  eliminate  waste. 

Inspiration  —  Process  of  taking  air 

into  lungs. 
Expiration  —  Process  of  expelling 

air  from  lungs. 
External        oxygen  f 

supply  Takes  Place 

External  carbon  di-  ] 

oxide  elimination  [     lungs- 
Internal         oxygen 

supply 

Internal  carbon  di- 
oxide elimination 

Elevation 

ribs. 

Descent       of 
diaphragm. 
Lungs  expand. 

Mechanism  Air  rushes  in  through  trachea  and  bronchi, 

of  Inspira-  f  Inspiratory 

tion  and  muscles  re- 

Expiration  lax. 

Chest  cavity  made  smaller 


Processes  < 


Breathing 


External 
Respiration 


Internal 
Respiration 


Inspiration 


Cause  of 
Respiration 


Expiration 


Chest  cavity  enlarged 


Takes  place 
in  the 
cells. 

of 


Recoil  of  elas- 
tic thorax. 
Recoil  of  elas- 
tic lungs. 

Air  forced  out  through  trachea. 
Respiratory  centre  —  Action  is  automatic.     Assumed 
to  be  in  connection  with  all  the  cranial  and  spinal 
nerves. 

Inspiratory  —  tend       to 

increase  rate. 
Expiratory  —  check 


Rate  and  rhythm 
controlled  by 


Vagi 


nerves 


the 

action   of  the  inspira- 
tory  set. 
Carbon  dioxide  content  of  blood. 


270 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIII 


Cause  of 
First  Respi- 
ration 


Respiratory 
Rate 

Effect  of 
Respiration 
upon  the 
Blood 

Capacity  of 
Lungs 

Movement  of 
Residual  Air 
Maintained  by 

Effect  of 
Respiration 
upon  the 
Air  outside 
the  Body 

Proper  Ven- 
tilation 


Abnormal 
Types 

of 
Respiration 


'  1.  Increased  amount  of  carbon  dioxide  due  to  cutting  of 

the  umbilical  cord. 

2.  Reflex,  due  to  stimulation  of  the  sensory  nerves  of  the 
skin. 

Muscular  exercise. 

Emotion. 
Influenced  by 


18  times  per  minute. 
Ratio  to  pulse  1  to  4. 


A  little  more  than 
1  gallon  of  -air 
(4500  c.c.) 


Vital  capacity 
3700  c.c. 


Heart-beat. 
Age. 

1.  Loses  about  10%  of  carbon  dioxide. 

2.  Gains  about  10%  j  Oxyhaemoglobin. 

of  oxygen  1  Scarlet  color. 

3.  Temperature  is  slightly  reduced. 

Tidal 

Complemental 
Reserve 
Residual 

1.  Alternate  expansion  and  collapse  of  lungs. 

2.  Convection  currents. 

3.  Pulsation  of  the  arteries. 

4.  Diffusion  of  gases. 

1 .  Temperature  increased.     Expired  air  is  as  hot  as  blood. 

2.  Moisture  increased.     Expired  air  is  saturated  with 

moisture. 

3.  Oxygen  decreased  by  4.94%. 

4.  Carbon  dioxide  increased  by  4.34%. 

1.  Continuous  movement  of  the  air. 

2.  The  temperature  and  degree  of  humidity  must  favor 

the  evaporation  of  perspiration  from  the  skin. 

3.  Disagreeable  odors  must  be  eliminated. 
Dyspncea  —  difficult  breathing. 
Hyperpncea  —  excessive  breathing. 
Apnoea  —  lack  of  breathing. 


Cheyne-Stokes 


(Edematous  —  air 
rattling  sounds. 
Asphyxia  —  oxygen  starvation. 


1 .  Respirations  increase  in  force  and 

frequency,  then  gradually  de- 
crease and  stop.  Cycle  re- 
peated. 

2.  Respirations  increase  in  force  and 

frequency  up  to  a  certain  point, 
then  stop.     Cycle  repeated, 
cells   filled  with   fluid,   hence  moist, 


-. 


CHAPTER  XIV 

THE  DIGESTIVE  SYSTEM:  ALIMENTARY  CANAL  AND  ACCESSORY 

ORGANS 

IN  complex  multicellular  bodies,  the  cells  where  food  is  needed 
are  so  far  removed  from  the  points  of  entrance  of  food  material, 
that  it  is  necessary  that  these  foods  should  be  changed  physically 
and  chemically  into  such  standard  substances  as  can  diffuse  into 
the  blood  system  and  be  carried  by  the  blood  to  all  the  cells  of 
the  body  and  diffuse  into  them.  Chemical  and  physical  changes 
necessary  to  reduce  our  varied  foods  to  such  standard  substances 
as  the  tissues  can  use  are  effected  in  certain  organs  that  are  grouped 
together  and  called  the  digestive  system. 

THE  DIGESTIVE  SYSTEM 

The  digestive  system  consists  of  the  alimentary  canal  and 
the  accessory  organs :  (1)  the  salivary  glands,  (2)  the  tongue, 
(3)  the  teeth,  (4)  the  pancreas,  and  (5)  the  liver. 

ALIMENTARY  CANAL 

The  alimentary  canal  is  a  continuous  tube  which  extends  from 
the  mouth  to  the  anus.  It  measures  about  30  feet  (9  m.)  in  length, 
the  greater  part  being  coiled  up  in  the  cavity  of  the  abdomen. 
The  portion  above  the  diaphragm  is  composed  of  three  coats; 
and  the  portion  below  the  diaphragm  is  composed  of  four  coats. 
Beginning  at  the  inner  lining  these  coats  are :  — 

(1)  The  mucous.  f  Both  described  in 

(2)  The  areolar  or  sub-mucous.  {  Chapter  VIII 

(3)  The  muscular  coat  consists  almost  entirely  of  non-striated 
muscular  tissue,  usually  arranged  in  two  layers.      The  internal 
cells  are   circular  in  direction,  and  the  external  cells  run  longi- 
tudinally.    By  the  alternate  contraction  and  relaxation  of  cells 
arranged  in  this  fashion  (the  contractions  starting  from  above), 
the  contents  of  the  tube  are  propelled  from  above  downward. 

(4)  The  serous  coat  is  derived  from  the  peritoneum. 

271 


272  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 

The  peritoneum.  —  This  is  the  largest  serous  membrane  in  the 
body  and  in  the  male  consists  of  a  closed  sac,1  the  parietal  layer  of 
which  lines  the  walls  of  the  abdominal  cavity ;  the  inner  or  vis- 
ceral layer  is  reflected  over  the  abdominal  organs,  and  the  upper 
surface  of  some  of  the  pelvic  organs.  The  arrangement  of  the  peri- 
toneum is  very  complex,  for  several  elongated  sacs  and  double 
folds  extend  from  it,  to  pass  in  between  and  either  wholly  or 
partially  surround  the  viscera  of  the  abdomen  and  pelvis.  One 
important  fold  is  the  omentum,  which  hangs  like  a  curtain  in  front 
of  the  stomach  and  the  intestines ;  another  is  the  mesentery,  which 
is  a  continuation  of  the  serous  coat  and  attaches  the  small  and 
much  of  the  large  intestine  to  the  spine. 

When  the  abdominal  cavity  is  opened,  the  intestines  appear  to 
lie  within  the  cavity  like  a  loose  coil  of  rope.  If,  however,  an 
attempt  is  made  to  lift  a  coil  from  its  place  a  clear,  glistening 
sheet  of  tissue  is  found  attached  to  it.  This  is  the  mesentery. 
The  posterior  portion  is  gathered  into  folds  which  are  attached 
to  the  spine  along  a  short  line  of  insertion  which  results  in  a  struc- 
ture that  has  the  appearance  of  a  ruffle  or  flounce. 

Functions  of  the  peritoneum.  —  Like  all  serous  membranes  the 
peritoneum  serves  to  prevent  friction  between  contiguous  organs 
by  secreting  serum  which  acts  as  a  lubricant.  To  a  limited  ex- 
tent it  serves  to  hold  the  abdominal  and  pelvic  organs  in  position, 
also  unites  and  separates  these  organs.  In  addition  to  these  func- 
tions, the  omentum  usually  contains  fat,  and  serves  to  keep  the 
organs  it  covers  warm. 

Divisions  of  the  alimentary  canal.  —  For  convenience  of  descrip- 
tion, the  alimentary  canal  may  be  divided  into :  - 

Mouth,  containing  tonsils,  tongue,  salivary  glands,  and  teeth. 

Pharynx. 

(Esophagus. 

Stomach. 

f  Duodenum. 
Small  or  thin  intestine    j  Jejunum. 

I  Ileum. 


Caecum. 

Large  or  thick  intestine  j  Colon.  - 
[  Rectum. 


Ascending. 

Transverse. 

Descending. 


1  In  the  female  the  peritoneum  is  not  a  closed  sac,  because  the  Fallopian  tubes 
open  into  it  at  their  extremities. 


CHAP.  XIV]         THE  DIGESTIVE  SYSTEM 


273 


MOUTH,   OR  BUCCAL  CAVITY 

The  mouth  cavity  is  a  nearly  oval-shaped  cavity  with  a  fixed 
roof  anteriorly,  a  flexible  roof  posteriorly,  and  a  movable  floor.  It 
is  bounded  in  front  by  the  lips,  on  the  sides  by  the  cheeks,  below 
by  the  tongue,  and  above  by  the  palate. 

The  palate.  —  The  palate  consists  of  a  hard  portion  in  front 
formed  by  bone1  covered  by  mucous  membrane,  and  of  a  soft 
portion  behind  containing  no  bone.  The  hard  palate  forms  the 
partition  between  the  mouth  and  nose;  the  soft  palate  arches 
backward  and  hangs  like  a 
curtain  between  the  mouth 
and  the  pharynx.  Hanging 
from  the  middle  of  its  lower 
border  is  a  pointed  portion 
of  the  soft  palate  called  the 
uvula  (little  grape). 

Fauces.  —  The  fauces  is 
the  name  given  to  the  aper- 
ture leading  from  the  mouth 
into  the  pharynx,  or  throat 
cavity. 

Pillars  of  the  fauces.  — 
From  the  base  of  the  uvula 
on  either  side  there  passes 
a  curved  fold  of  muscular 
tissue  covered  by  mucous 
membrane,  which  shortly 
after  leaving  the  uvula  is, 
as  it  were,  split  into  two  pil- 
lars, the  one  going  outward, 
downward,  and  forward, 
passing  to  the  side  of  the  tongue,  the  other  outward,  downward, 
and  backward  to  the  side  of  the  pharynx.  These  pillars  are 
known  respectively  as  the  anterior  and  the  posterior  pillars  of  the 
fauces. 

Tonsils.  —  In  the  lower  part  of  the  triangular  space  between 
the  anterior  and  posterior  pillars,  on  either  side,  lie  the  small  masses 


FIG.  161.  —  THE  SOFT  PALATE  AND  TON- 
SILLAR  REGIONS.     (Gerrish.) 


Processes  of  the  maxillae  and  palate  bones. 


274 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 


of  lymphoid  tissue  called  tonsils.  They  consist  of  a  collection  of 
lymph  nodules  held  together  by  a  distinct  capsule  and  covered 
on  their  exposed  surface  by  mucous  membrane. 

Function.  —  The  function  of  the  tonsils  is  imperfectly  under- 
stood. They  may  be  a  source  of  lymphocytes  and  leucocytes,  or 
they  may  act  as  filters  and  prevent  the  entrance  of  microorgan- 
isms. Inflammation  of  the  tonsils  is  called  tonsillitis. 

The  palate,  uvula,  pillars  of  the  fauces,  and  tonsils  are  plainly 
seen  if  the  mouth  is  widely  opened  and  the  tongue  depressed. 

The  tongue.  —  The  tongue  1  is  the  special  organ  of  the  sense  of 
taste  and  assists  in  speech.  It  has  also  to  be  considered  with  ref- 
erence to  digestion,  (1)  because  stimulation  of  the  nerves  of  the 

sense  of  taste  starts  the 
secretion  of  digestive 
fluids,  (2)  it  assists  in 
swallowing,  and  (3)  the 
follicles  at  the  back 
of  the  tongue  secrete 
mucus,  which  lubricates 
the  food  and  makes 
swallowing  easier. 
The  salivary  glands. 
-  The  mucous  mem- 
brane lining  the  mouth 
contains  many  minute 
glands  consisting  of  just 
one  cell.  These  are 
called  goblet  cells  and 
pour  their  secretion 
upon  its  surface,  but 

the  chief  secretion  of  the  mouth  is  supplied  by  the  salivary 
glands,  which  are  three  pairs  of  compound  saccular  glands  called 
the  parotid,  submaxillary,  and  sublingual,  respectively.  Each 
parotid  gland  is  placed  just  under  and  in  front  of  the  ear;  its 
duct  (Stenson's)  passes  forward  along  the  cheek,  until  it  opens  into 
the  interior  of  the  mouth  opposite  the  second  molar  tooth  of  the 
upper  jaw.  The  submaxillary  and  sublingual  glands  are  situ- 
ated below  the  jaw  and  under  the  tongue,  the  submaxillary  being 

1  A.  detailed  description  of  the  tongue  will  be  found  in  Chapter  XX. 


FIG.  162.  —  THE  SALIVARY  GLANDS. 


CHAP.  XIV]         THE  DIGESTIVE  SYSTEM 


275 


placed  farther  back  than  the  sublingual.  One  duct  from  each  sub- 
maxillary  and  a  number  of  small  ducts  from  each  sublingual 
open  in  the  floor  of  the  mouth  beneath  the  tongue.  The  secretion 
of  these  salivary  glands,  mixed  with  that  of  the  small  glands  of 
the  mouth,  is  called  saliva. 

Secretory  nerves.  —  The  salivary  glands  receive  a  double  nerve 
supply,  —  in  part  from  the  cranial  nerves  and  in  part  from  the 
sympathetic  system.  These  nerves  are  called  secretory  because 
they  control  the  activity  of  the  cells  which  form  the  secretion. 
Not  only  are  secretory  nerves  distributed  to  these  glands,  but 
vasomotor  fibres  are  contained  in  the  same  nerves.  The  cranial 
nerves  contain  vaso-dilator  fibres.  Stimulation  of  these  causes  a 
dilatation  of  the  small  arteries  and  an  increased  blood-flow; 
while  the  sympathetic  carries  vaso-constrictor  fibres  that  constrict 
the  arteries  and  diminish  the  blood-flow. 

The  teeth.  —  The  semicircular  borders  of  the  upper  and  lower 
jaw-bones  (the  alveolar  processes)  contain  sockets  for  the  recep- 
tion of  the  teeth.  A  dense,  insensitive,  fibrous  membrane  covered 
by  smooth  mucous  membrane  —  the  gums  —  covers  these  pro- 
cesses and  extends  a  little 
way  into  each  socket. 
These  sockets  are  lined 
by  periosteum,  which 
connects  with  the  gums 
and  serves  (1)  to  attach 
the  teeth  to  their  sockets, 
and  (2)  as  a  source  of 
nourishment. 

Each  tooth  consists  of 
three  portions :  (1)  the 
root,  consisting  of  one  or 
more  fangs  contained  in 
the  socket ;  (2)  the  crown, 
which  projects  beyond 
the  level  of  the  gums;  and  (3)  the  neck  or  constricted  portion 
between  the  root  and  the  crown,  which  is  enveloped  by  the  gum. 

Each  tooth  is  composed  principally  of  dentine,  which  gives  it 
shape  and  encloses  a  cavity,  the  pulp  cavity.  The  dentine  of  the 
crown  is  capped  with  a  dense  layer  of  enamel.  The  dentine  of  the 


CROWN 


NECK 


ROOT 


ENAMEL 


PULP  CAVITY 
DENTINE 


CEMENT 


CANAL  IN  ROOT 


FIG.  163.  —  SECTION  OF  HUMAN  MOLAR 
TOOTH.     (Adapted  from  Dalton.) 


276  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 

root  is  covered  by  cement.  These  three  substances,  enamel, 
dentine,  and  cement,  are  all  harder  than  bone,  enamel  being 
the  hardest  substance  found  in  the  body.  They  are  developed 
from  epithelial  tissue.  The  pulp  cavity  is  just  under  the  crown  and 
is  continuous  with  a  canal  that  traverses  the  centre  of  each  root, 
and  opens  by  a  small  aperture  at  its  extremity.  It  is  filled  with 
dental  pulp,  which  consists  of  loose  connective  tissue  holding  a 
number  of  blood-vessels  and  nerves  which  enter  by  means  of  the 
canal  from  the  root. 

There  are  two  sets  of  teeth  developed  during  life :  the  first, 
temporary  or  deciduous ;  and  the  second,  permanent. 

Temporary  teeth.  —  In  the  first  set  are  twenty  teeth,  ten  in 
each  jaw :  four  incisors,  two  canines,  and  four  molars.  The  cut- 
ting of  the  temporary  teeth  usually  begins  at  six  months  and 
ends  at  about  the  age  of  two  years.1  In  nearly  all  cases  the  teeth 
of  the  lower  jaw  appear  before  the  corresponding  ones  of  the  upper 

jaw. 

TEMPORARY  TEETH 

MOLARS 

Upper 
Lower 

Permanent  teeth.  —  During  childhood  the  temporary  teeth  are 
replaced  by  the  permanent.  In  the  second  set  are  thirty-two 
permanent  teeth,  sixteen  in  each  jaw.  The  first  molar  usually 
appears  between  five  and  seven  years  of  age.2 

PERMANENT  TEETH 

MOLAR       BICUSPIE 

Upper 
Lower 

1  The  temporary  teeth  are  usually  cut  in  the  following  order:  — 

Lower  central  incisors        6  to    9  months 

Upper  incisors 8  to  10  months 

Lower  lateral  incisors  and  first  molars     .     .     .     .      15  to  21  months 

Canines       . 16  to  20  months 

Second  molars 20  to  24  months 

2  The  permanent  teeth  appear  at  the  following  periods:  — 

First  molars 6^  years 

Two  middle  incisors 7th  year 

Two  lateral  incisors 8th  year 

First  bicuspid       .     .     .     .  ' 9th  year 

Second  bicuspid        10th  year 

Canine llth  to  12th  year 

Second  molars 12th  to  13th  year 

Third  molars        .     .     ..     ,     ,,,.„,,,  17th  to  21st  year 


MOLARS 

CANINE 

INCISORS 

CANINE 

MOLARS 

2 

1 

4 

1 

2 

2 

1 

4 

1 

2 

MOLAR 

BICUSPID 

CANINE 

INCISOR 

CANINE 

BICUSPID 

MOLAR 

3 

2 

1 

4 

1 

2 

3 

3 

2 

1 

•4 

1 

2 

3 

CHAP.  XIV]          THE   DIGESTIVE  SYSTEM  277 

According  to  their  shape  and  use  the  teeth  are  divided  into 
incisors,  canines,  bicuspids,  and  molars. 

Incisors  are  eight  in  number  and  form  the  four  front  teeth 
of  each  jaw.  They  have  wide,  sharp  edges,  and  are  specially 
adapted  for  cutting  food. 

Canines  are  four  in  number,  two  in  each  jaw.  The  upper 
canines  are  commonly  called  eye-teeth ;  the  lower,  stomach  teeth. 
They  have  sharp,  pointed  edges  and  are  longer  than  the  incisors. 
In  the  human  being  they  serve  the  same  purpose  as  the  incisors. 

Bicuspids  are  eight  in  number  in  the  permanent  set.  There 
are  none  in  the  temporary  set.  There  are  four  in  each  jaw,  two 
being  placed  just  behind  each  of  the  canine  teeth. 

They  are  broad,  with  two  points  or  cusps  on  each  crown ;  these 
teeth  have  only  one  root ;  the  root,  however,  being  more  or  less 
completely  divided  into  two.  Their  function  is  to  cut  and  grind 
food. 

Molars  are  twelve  in  number  in  the  permanent  set,  and  only 
eight  in  the  temporary  set. 

The  molars,  or  true  grinders,  have  broad  crowns  with  small, 
pointed  projections,  which  make  them  well  fitted  for  crushing  and 
bruising  the  food  :  they  each  have  two  or  three  roots.  The  twelve 
molars  do  not  replace  the  temporary  teeth,  but  are  gradually 
added  with  the  growth  of  the  jaws ;  the  last  or  hindmost  molars 
may  not  appear  until  twenty-one  years  of  age;  hence  called 
late  teeth  or  wisdom  teeth." 

Function.  —  The  teeth  assist  in  the  process  of  mastication  by 
cutting  and  grinding  the  food.  It  might  be  thought  that  the 
vigorous  employment  of  the  teeth  for  this  purpose  would  only 
hasten  their  wear  and  tear.  This  may  be  true  at  a  time  when 
their  life  is  nearly  extinct,  but  at  an  earlier  period  mastication 
is  good  for  the  teeth  because  they  are  made  to  sink  and  rise  in 
their  sockets  with  a  massaging  effect  upon  the  gums  which  tends 
to  promote  circulation  in  the  pulp. 

THE   PHARYNX 

The  pharynx,  or  throat  cavity,  is  that  part  of  the  alimentary 
canal  which  is  behind  the  nose,  mouth,  and  larynx.  It  is  a  mus- 
culo-membranous  tube  shaped  somewhat  like  a  cone,  with  its 
broad  end  turned  upward  and  its  constricted  end  downward 


278  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XIV 

to  end  in  the  oesophagus.  It  is  about  five  inches  (12.5  cm.)  in 
length.  Above,  it  is  attached  to  the  base  of  the  skull,  and 
behind,  to  the  cervical  vertebrae ;  in  front  and  on  each  side  are 
apertures  which  communicate  with  the  nose,  ears,  mouth,  and 
larynx. 

Of  these  apertures  there  are  seven :  — 

Two  in  front  above,  leading  into  the  back  of  the  nose,  the 
posterior  nares. 

Two,  one  on  either  side  above,  leading  into  the  Eustachian 
tubes,  which  communicate  with  the  ears. 

One  midway  in  front,  the  fauces. 

Two  below,  one  opening  into  the  larynx  and  the  other  into  the 
oesophagus. 

The  mucous  membrane  lining  the  pharynx  is  well  supplied 
with  glands,  and  at  the  back  of  the  cavity  there  is  a  considerable 
mass  of  lymphoid  tissue.  During  infancy  and  childhood  this  may 
increase  to  such  an  extent  that  it  interferes  with  nasal  breathing. 
The  child  is  then  said  to  have  adenoids  and  is  obliged  to  breathe 
through  the  mouth ;  hence  the  term  "  mouth  breathers." 

Function.  —  The  muscular  tissue  in  the  walls  of  the  pharynx  is 
of  the  striped  variety,  and  when  the  act  of  swallowing  is  about  to 
be  performed,  the  muscles  draw  the  pharynx  upward  and  dilate 
it  to  receive  the  food ;  they  then  relax,  the  pharynx  sinks,  and 
the  other  muscles  contracting  upon  the  food,  it  is  pressed  down- 
ward and  onward  into  the  oesophagus. 

THE  (ESOPHAGUS,   OR  GULLET 

The  oesophagus  is  a  comparatively  straight  tube,  about  nine 
inches  (22.  cm.)  long,  which  commences  at  the  lower  end  of  the 
pharynx,  behind  the  trachea.  It  descends  in  front  of  the  spine, 
passes  through  the  diaphragm,  and  terminates  in  the  upper  or 
cardiac  end  of  the  stomach. 

Structure.  —  The  walls  of  the  oesophagus  are  composed  of  three 
coats :  (1)  an  external  or  muscular,  (2)  a  middle  or  areolar,  and 
(3)  an  internal  or  mucous,  coat.  The  muscular  coat  is  arranged 
in  an  external  longitudinal  and  an  internal  circular  layer.  Con- 
traction of  the  outer  layer  produces  dilatation  of  the  tube ;  con- 
traction of  the  inner,  constriction.  Consequently  this  arrange- 


CHAP.  XIV]         THE  DIGESTIVE  SYSTEM 


279 


ment  is  of  importance  in  the  movements  which  carry  the  food  from 
the  pharynx  to  the  stomach.  These  movements  are  called  peri- 
staltic, and  consist  of  contractions  of  the  longitudinal  layer,  fol- 
lowed by  contractions  of  the  circular  layer.  The  areolar  coat  serves 
to  connect  the  muscular  and  mucous  coats.  The  mucous  mem- 


RIGHT 
HYPOCHON- 
DRIAC 
REGION 


RIGHT 
LUMBAR 
REGION 


RIGHT 
ILIAC 
EGION 


LEFT 

HYPOCHON- 
DRIAC 

REG.ON          ._jCARTrtAGE 
OF  TENTH  RIB 


UMBILICAL 


REGION 


HIGHEST  LEVEt 
F  ILIAC  CREST 


•ANT.  SUP. 
ILIAC  SPINE 


HYPOGASTRIC 
REGION 


FIG.  164.  —  REGIONS  OF  THE  ABDOMEN.  (Gerrish.)  The  following  structures 
are  found  within  the  cavity :  —  1.  The  greater  part  of  the  alimentary  canal,  viz., 
stomach,  small  intestine,  and  large  intestine.  2.  Digestive  glands  :  the  liver  and 
pancreas.  3.  Ductless  glands :  the  spleen  and  the  two  supra-renal  glands. 
4.  Urinary  apparatus  :  the  kidneys,  ureters,  bladder  and  part  of  urethra.  5.  The 
internal  generative  organs,  according  to  the  sex.  6.  Blood-vessels  and  lymph 
vessels,  and  lymph  nodes.  7.  The  abdominal  portion  of  the  central  and  sympa- 
thetic nervous  systems.  8.  The  peritoneum  —  the  serous  membrane  which  lines 
the  cavity,  and  is  reflected  over  most  of  its  contained  viscera. 

brane  is  disposed  in  longitudinal  folds  which  disappear  upon  dis- 
tent ion  of  the  tube. 

Function.  —  The  oesophagus  serves  (1)  to  connect  the  pharynx 
with  the  stomach,  and  (2)  to*  receive  the  food  from  the  pharynx 
and  by  a  series  of  peristaltic  contractions  pass  it  on  to  the 
stomach. 

Regions  of  the  abdomen.  —  That  portion  of  the  alimentary 
canal  which  is  below  the  thorax  is  contained  in  the  abdomen. 
For  convenience  of  description,  the  abdomen  may  be  artificially 


280 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 


divided   into   nine   regions   by   drawing  the   following  arbitrary 
lines :  — 

1.  Draw  a  circular  line  around  the  body  at  the  level  of  the 
tenth  costal  cartilages. 

2.  Draw  another  circular  line  at  the  level  of  the  anterior  superior 
spines  of  the  ilia. 

3.  Draw  a  vertical  line  on  each  side  from  the  centre  of  Poupart's 
ligament  upward. 

These  lines  are  to  be  considered  as  edges  of  planes  which  divide 
the  abdomen  into  the  nine  regions  illustrated  in  Fig.  164. 

THE   STOMACH 

After  the  ossophagus  perforates  the  diaphragm  it  ends  in  the 
stomach  (gaster),  which  is  the  most  dilated  portion  of  the  alimen- 
tary canal  and  serves  as  a  temporary  receptacle  for  food.  It  lies 
obliquely  or  horizontally  in  the  epigastric  and  left  hypochondriac 


PYLOR 


FUNGUS 


INTERMEDIATE 
REGION 


FIG.  165.  —  FORM  AND  OUTLINE  OF  THE  STOMACH  AT  DIFFERENT  STAGES  OF 
DIGESTION.  A,  when  empty  and  contracted.  B,  at  an  early  stage  of  gastric 
digestion. 

regions  of  the  abdomen,  directly  under  the  diaphragm.  The  shape 
and  position  of  the  stomach  are  modified  by  changes  within  itself, 
and  in  the  surrounding  organs.  These  modifications  are  deter- 
mined by  (1)  the  amount  of  the  stomach  contents,  (2)  the  stage  of 
digestion  which  has  been  reached,  (3)  the  degree  of  development 
and  power  of  the  muscular  walls,  and  (4)  the  condition  of  the  ad- 
jacent intestines.  When  empty  or  contracted  the  shape  of  the 
stomach  is  comparable  to  a  sickle  or  sausage.  At  an  early  stage 
of  gastric  digestion,  the  stomach  usually  consists  of  two  segments, 


CHAP.  XIV]         THE  DIGESTIVE  SYSTEM 


281 


a  large  globular  portion  on  the  left,  and  a  narrow  tubular  portion 
on  the  right.  When  distended  with  food  it  has  the  shape  shown 
in  Fig.  166. 


FIG.  166.  —  THE  STOMACH  AND  INTESTINES,  FRONT  VIEW,  THE  GREAT  OMEN- 
TUM  HAVING  BEEN  REMOVED,  AND  THE  LIVER  TURNED  UP  AND  TO  THE  RIGHT.  The 
dotted  line  shows  the  normal  position  of  the  anterior  border  of  the  liver.  (Gerrish.) 

The  stomach  presents  two  openings  and  two  borders  or  curva- 
tures. 

Openings.  —  The  opening  by  which  the  oesophagus  communi- 
cates with  the  stomach  is  known  as  the  cardiac  or  oesophageal 
orifice,  and  the  orifice  which  communicates  with  the  duodenum  is 
known  as  the  pyloric.  Both  the  cardiac  and  pyloric  apertures  are 
guarded  by  strong  bands  of  muscle  which  are  in  a  state  of  qqntrac- 


282  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 

tion  during  digestion.  By  this  arrangement,  the  food  is  kept  in 
the  stomach  until  it  is  ready  for  intestinal  digestion,  when  the 
circular  fibres  guarding  the  pyloric  aperture  relax.  The  acidity 
of  the  stomach  contents  seems  to  produce  this  relaxation. 

Curvatures.  —  In  all  positions  the  stomach  is  more  or  less  curved 
upon  itself.  A  line  drawn  from  the  cardiac  orifice  along  the  con- 
cave border  to  the  pyloric  orifice  is  said  to  follow  the  lesser  curva- 
ture. A  much  longer  line  connecting  the  same  points,  but  follow- 
ing the  convex  border,  defines  the  greater  curvature. 

Component  parts.  —  The  fund  us  is  the  blind  rounded  end  of  the 
stomach  to  the  left  of  the  heart.  The  opposite  or  smaller  end  is 
called  the  pyloric  extremity  and  lies  under  the  liver.  The  central 
portion  between  the  fundus  and  pyloric  extremity  is  called  the 
intermediate  region. 

Structure.  —  The  wall  of  the  stomach  consists  of  four  coats : 
(1)  serous,  (2)  muscular,  (3)  submucous  or  areolar,  and  (4)  mucous. 

(1)  The  serous  coat  is  formed  by  a  fold  of  the  peritoneum. 
This  fold  is  thrown  over  the  stomach  and  covers  it  before  and 
behind.  The  anterior  and  posterior  folds  unite  at  the  lower  border 
and  form  an  apron-like  appendage,  the  omentum,  which  is  sus- 
pended in  front  of  the  intestines. 

(2)  The  muscular  coat  of  the  stomach  is  beneath  the  serous 
coat  and  closely  connected  with  it.     It  consists  of  three  layers  of 
unstriped  muscular  tissue  :  an  outer,  longitudinal  layer ;  a  middle 
or  circular  layer;    and   an    inner,   less    well-developed,   oblique 
layer. 

(3)  The  submucous  coat  consists  of  loose  areolar  tissue  con- 
necting the  muscular  and  mucous  coats.     It  carries  nerves  and 
vessels. 

(4)  The  mucous  coat  is  very  soft  and  thick,  the  thickness  being 
mainly  due  to  the  fact  that  it  is  densely  packed  with  small  glands. 
It  is  covered  with  columnar  epithelium,  and  in  its  undistended 
condition  is  thrown  into  folds  or  rugae.     The  surface  is  honey- 
combed by  tiny,  shallow  pits,  into  which  the  ducts  or  mouths  of 
the  glands  open. 

Gastric  glands.  —  The  gastric  glands  are  of  three  varieties, 
(1)  cardiac ;  (2)  true  gastric  or  peptic ;  and  (3)  pyloric. 

(1)  Cardiac  glands  are  simple  tubular  glands  found  about  the 
cardiac  or  cesophageal  orifice.  They  secrete  mucus. 


CHAP.  XIV]         THE  DIGESTIVE   SYSTEM 


283 


PARIETAL  CELLS 


(2)  True  gastric  or  peptic  glands  are  simple  tubular  glands 
distributed  throughout  the  fundus  and  intermediate  region  of  the 
stomach  and  may  even  be  found  at  the  pylorus.     These  glands 
are  lined  by  epithelial  cells  of  which  there  are  two  varieties,     (a) 
One  variety  of  cell  is  found  lining  the  lumen  of  the  tube.     These 
are  called  chief  cells  and  se- 
crete pepsinogen.     (6)  A  sec- 
ond variety  called  parietal  cells 

are    found    behind   the    chief 

cells,  where  they  do  not  come 

in    contact    with    the  lumen. 

These  cells  secrete  acid,  and 

pepsinogen    in    the    presence 

of    acid     is     converted     into       B8^BB8S^CHIEF  CELLS 

pepsin. 

(3)  Pyloric  glands  are 
branched  tubular  glands  found 
most    plentifully    about     the 
pylorus.     They    secrete    pep- 
sinogen and  mucus. 

The  combined  secretion  of 
these  glands  forms  the  gastric 
fluid. 

Nerves  and  blood-vessels.  —  The  stomach  is  supplied  with 
nerves  from  the  sympathetic  system,  and  also  with  branches  from 
the  vagus  nerve,  which  comes  from  the  central  nervous  system. 
The  blood-vessels  are  derived  from  the  three  divisions  of  the  coeliac 
axis,  i.e.,  gastric,  and  branches  of  the  hepatic  and  splenic. 

Functions. — The  functions  of  the  stomach  are  (1)  to  connect 
the  oesophagus  with  the  intestine,  (2)  to  receive  the  food  and  hold 
it  while  it  undergoes  certain  mechanical  processes  which  reduce 
it  to  the  consistency  of  thick  soup,  and  also  while  it  undergoes 
certain  chemical  changes  brought  about  by  secretion  of  the  gastric 
glands,  (3)  to  secrete  mucus  and  gastric  fluid. 

THE   SMALL,    OR   THIN,    INTESTINE 

The  small  intestine  extends  from  the  stomach  (pyloric  valve) 
above  to  the  large  intestine  (valve  of  the  colon)  below.  It  is  a 
convoluted  tube  about  twenty  feet  (6  m.)  in  length,  and  fills 


LUMEN 


FIG.  167.  —  PORTION  or  TRUE  GASTRIC 
OR  PEPTIC  GLAND. 


284  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 

the  greater  part  of  the  front  abdominal  cavity.  Its  diameter  at 
the  beginning  is  about  two  inches  (5  cm.),  but  it  gradually  dimin- 
ishes in  size  and  is  hardly  an  inch  (2.5  cm.)  in  diameter  at  its 
lower  end.  The  small  intestine  is  divided  by  anatomists  into 
three  portions  :  —  the  duodenum,  jejunum,  and  ileum. 

The  duodenum.  —  The  duodenum  is  twelve  fingers'  breadth 
in  length  (ten  inches  or  25  cm.),  and  is  the  widest  part  of  the  small 
intestine.  It  extends  from  the  pyloric  end  of  the  stomach  to  the 
jejunum. 

Beginning  at  the  pylorus,  the  duodenum  at  first  passes  up- 
ward and  backward  to  the  under  surface  of  the  liver ;  it  then 
makes  a  complete  bend  and  passes  downward  in  front  of  the 
kidney ;  it  again  turns  in  a  right  angle  direction  to  the  left  and 
passes  horizontally  across  the  front  of  the  vertebral  column. 
This  third  portion  of  the  duodenum  lies  retroperitoneally, 
so  that  only  its  anterior  aspect  is  covered  by  peritoneum.  The 
small  intestine  now  passes  forward  so  as  to  leave  the  posterior 
abdominal  wall,  and  becomes  completely  invested  by  peritoneum 
and  has  a  true  mesentery.  The  point  at  which  it  becomes 
completely  invested  by  peritoneum  marks  the  termination  of 
the  duodenum  and  the  beginning  of  the  jejunum. 

The  jejunum.  —  The  jejunum  or  empty  intestine,  so  called 
because  it  is  always  found  empty  after  death,  constitutes  about 
two-fifths  of  the  remainder,  or  seven  and  a  half  feet  (2.2  m.),  of 
the  small  intestine,  and  extends  from  the  duodenum  to  the  ileum. 

The  ileum.  —  The  ileum,  or  twisted  intestine,  so  called  from  its 
numerous  coils,  constitutes  the  remainder  of  the  small  intestine, 
and  extends  from  the  jejunum  to  the  large  intestine,  which  it  joins 
at  a  right  angle. 

There  is  no  definite  landmark  to  determine  the  point  at  which 
the  jejunum  ceases  and  the  ileum  begins,  although  the  mucous 
membrane  of  the  one  differs  somewhat  from  the  mucous  mem- 
brane of  the  other;  the  change  is  a  gradual  transition,  and  one 
structure  shades  off  into  the  other.  The  lengths  in  feet  as  given 
are  arbitrary,  but  those  usually  accepted. 

Coats  of  the  small  intestine.  —  The  small  intestine  has  four 
coats,  which  correspond  in  character  and  arrangement  with 
those  of  the  stomach. 

(1)  The  serous  coat  furnished  by  the  peritoneum  forms  an  al- 


CHAP.  XIV]         THE   DIGESTIVE   SYSTEM 


285 


FIG.  168.  —  PORTION  OF  SMALL  INTES- 
TINE LAID  OPEN  TO  SHOW  VALVUL^E  CON- 
NIVENTES.  Not  highly  enough  magnified  to 
show  villi  on  valvulse  conniventes.  (Col- 
lins.) 


most  complete  covering  for  the  whole  tube  except  for  part  of  the 
duodenum. 

(2)  The  muscular  coat  of  the  small  intestine  has  only  two  layers : 
an  outer,  thinner  and  longitudinal ;  and  an  inner,  thicker  and  cir- 
cular.    This  arrangement  is 

necessary  for  the  peristaltic 
action  of  the  intestine. 

(3)  The     submucous,     or 
areolar   coat,   carries   blood- 
vessels,     lymphatics,      and 
nerves. 

(4)  The    mucous    coat  is 
thick  and  very  vascular. 

Valvulce  conniventes.  — 
About  one  or  two  inches 
beyond  the  pylorus  the  mucous  and  submucous  coats  of  the  small 
intestine  are  arranged  in  circular  folds  called  valvulse  conni- 
ventes. Some  of  these 
folds  extend  all  the 
way  around  the  cir- 
cumference of  the  in- 
testine ;  others  extend 
only  one-half  or  one- 
third  of  the  way.  Un- 
like the  rugse  of  the 
stomach,  the  valvulse 
conniventes  do  not  dis- 
appear when  the  intes- 
tine  is  distended. 
About  the  middle  of 
the  jejunum  they  be- 
gin to  decrease  in  size, 
and  in  the  lower  part 
of  the  ileum  they 
almost  entirely  disap- 
pear. The  purpose  of  the  valvulse  conniventes  is  :  (1)  to  prevent 
the  food  from  passing  through  the  intestines  too  quickly,  and 
(2)  to  present  a  greater  surface  for  the  absorption  of  digested  food. 
Villi.  —  Throughout  the  whole  length  of  the  small  intestine  the 


COLUMNAR 
EPITHELIUM 


CAPILLARY""  /          'CAPILLARV 

NETWORK        LACTEAL' VESSEL     NETWORK 

FIG.  169.  —  AN  INTESTINAL  VILLUS. 
magnified.) 


(Highly 


286  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XIV 

mucous  membrane  presents  a  velvety  appearance  due  to  minute 
finger-like  projections  called  villi.  Each  villus  consists  of  a  cen- 
tral lymph  channel  called  a  lacteal,  surrounded  by  a  network  of 
blood  capillaries,  held  together  by  lymphoid  tissue.  This  in  turn 
is  surrounded  by  a  layer  of  columnar  cells.  After  the  food  has 
been  digested  it  passes  into  the  capillaries  and  lacteals  of  the 
villi,  so  that  this  arrangement  increases  the  surface  for  absorption. 
Glands  and  nodes  of  the  small  intestine.  —  Besides  these 
projections  formed  for  absorption  the  mucous  membrane  is  thickly 
studded  with  secretory  glands  and  nodes.  These  are  known  as  — 

1.  Simple  follicles  or  crypts  of  Lieberkuhn. 

2.  Duodenal  or  Brunner's  glands. 

,  ,     J  (a)  Solitary  lymph  nodules. 

3.  Lymph  nodules  |  (6)  Aggregated  lymph  nodules. 

(1)  Simple  follicles.  —  These  glands  are  found  over  every  part 
of  the  surface  of  the  small  intestine.     They  are  simply  tubular 


FIG.  170.  —  PORTION  OF  THE  Mucous  MEMBRANE,  FROM  THE  ILEUM. 
Moderately  magnified,  exhibiting  the  villi  on  its  free  surface,  and  between  them 
the  orifices  of  the  tubular  glands.  1,  portion  of  an  aggregated  lymph  nodule; 
2,  a  solitary  lymph  nodule  ;  3,  fibrous  tissue.  (Dalton.) 

depressions  in  the  mucous  membrane,  lined  with  columnar  epithe- 
lium. 

(2)  Duodenal    glands.  —  These    glands    are    better    known    as 
Brunner's   glands.     They   are    compound   glands   found    in   the 
submucous  tissue  of  the  duodenum.     The  simple  follicles  and  the 
duodenal  glands  secrete  the  intestinal  digestive  fluid   which  is 
named  the  succus  entericus. 

(3)  Lymph  nodules.  —  These  are  of  two  varieties,  (a)  solitary 
lymph  nodules,  (b)  aggregated  lymph  nodules  of  Peyer. 

(a)  Solitary  lymph  nodules.  —  Closely  connected  with  the  lym- 
phatic vessels  in  the  walls  of  the  intestines  are  small,  rounded 
bodies  of  the  size  of  a  small  pin's  head,  called  solitary  lymph 
nodules.  These  bodies  consist  of  a  rounded  mass  of  fine  lym- 


CHAP.  XIV]         THE   DIGESTIVE  SYSTEM 


287 


phoid  tissue,  the  meshes  of  which  are  crowded  with  leucocytes. 
Into  this  mass  of  tissue  one  or  more  small  arteries  enter  and  form 


PLANE  OF     f 
MUCOUS 
SURFACE 


-LAYER  OF  CIRCULAR  FIBRES/ 
|||  'LAYER  OF  .LONGITUDINAL  FIBRES' 

.JFiG.  171.  —  MUCOSA  OF  SMALL  INTESTINE  IN  IDEAL  VERTICAL  CROSS-SECTION. 

(Gerrish.) 

a  capillary  network,  from  which  the  blood  is  carried  away  by 
one  or  more  small  veins.  Surrounding  the  mass  are  lymph 
channels  which  are  continu- 
ous with  the  lymphatic  ves- 
sels in  the  tissue  below. 

Aggregated  lymph  nodules. 
—  They  are  simply  collec- 
tions of  lymph  nodules, 
commonly  called  Peyer's 
patches.  A  well-formed 
Peyer's  patch  consists  of 
fifty  or  more  of  these  soli- 
tary lymph  nodules,  ar-  Fm  172.  _  AGGREGATED  LYMPH  NODULE 
ranged  in  a  single  layer  (Peyer's  Patch).  (Gerrish.) 

close  under  the  epithelium 

of  the  intestinal  mucous   membrane,  and  stretching  well  down 
into  the  tissue  beneath.    These  patches  are  circular  or  oval  in 


288 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 


shape,  from  ten  to  sixty  in  number  and  vary  in  length  from  one- 
half  inch  to  four  inches  (1.25  to  10  cm.).  They  are  largest  and 
most  numerous  in  the  ileum.  In  the  lower  part  of  the  jejunum 
they  are  small  and  few  in  number.  They  are  occasionally  seen 
in  the  duodenum.  These  Peyer's  patches  are  the  seat  of  local 
inflammation  and  ulceration  in  typhoid  fever. 

Function.  —  It  is  in  the  small  intestine  that  the  greatest  amount 
of  digestion  and  absorption  takes  place.  The  valvulae  conniventes 
delay  the  food  so  that  it  is  more  thoroughly  subjected  to  the  action 
of  the  digestive  fluids ;  and  being  covered  with  villi  they  increase 
the  surface  for  absorption.  The  glands  of  the  small  intestine 
secrete  the  succus  entericus  which  aids  in  the  digestion  of  food. 

THE  LARGE,   OR  THICK,   INTESTINE 

The  largeness  of  the  next  division  of  the  alimentary  canal  is  in 
its  width,  not  in  its  length;  for  it  is  only  about  five  feet  (1.5  m.) 
long,  but  is  wider  than  the  small  intestine,  being  two  and  one- 
half  inches  (6.3  cm.)  in  its  broadest  part.  It  extends  from  the 
ileum 'to  the  anus.  Like  the  small  intestine,  it  is  divided  into 

three  parts :  the  caecum  with 
the  vermiform  appendix,  colon, 
and  rectum. 

The  caecum.  —  The  caecum 
(ccecus,  blind)  is  a  large  blind 
pouch  at  the  commencement  of 
the  large  intestine.  The  small 
intestine  opens  into  the  side 
wall  of  the  large  intestine  about 
two  and  a  half  inches  (6.3  cm.) 
aboye  the  commencement  of 
the  large  intestine.  This  two 
and  one-half  inches  of  large  in- 
testine form  a  cul-de-sac  below 
the  opening,  and  this  cul-de-sac 
is  called  the  caecum.  The  open- 
ing from  the  ileum  into  the 
large  intestine  is  provided  with 

two  large  projecting  lips  of  mucous  membrane  which  allow  the 
passage  of  material  into  the  large  intestine,  but  effectually  prevent 


FIG.  173.  —  CAVITY  OF  THE  C/ECUM, 
ITS  FRONT  WALL,  HAVING  BEEN  CUT 
AWAY.  The  valve  of  the  colon  (ileo- 
caecal)  and  the  opening  of  the  appendix 
are  shown.  (Gerrish.) 


CHAP.  XIV]         THE   DIGESTIVE   SYSTEM  289 

the  passage  of  material  in  the  opposite  direction.  These  mucous 
folds  form  what  is  known  as  the  valve  of  the  colon,  or  the  ileo- 
csecal  valve. 

The  vermiform  appendix  is  a  narrow,  wormlike  tube  about  the 
diameter  of  an  ordinary  lead  pencil,  and  from  three  t^ seven 
inches  (7.5  to  17.5  cm.)  long.  It  is  attached  to  the  lower  end  of 
the  caecum,  but  its  directions  and  relations  are  very  variable.  In 
a  general  way  it  may  be  said  to  be  located  in  the  right  iliac  region. 

The  colon.  —  The  colon,  though  one  continuous  tube,  is  sub- 
divided into  the  ascending,  transverse,  and  descending  colon,  with 
the  sigmoid  flexure.  The  ascending  portion  ascends  on  the  right 
side  of  the  abdomen  until  it  reaches  the  under  surface  of  the 
liver,  where  it  bends  abruptly  to  the  left  (right  colic  or  hepatic 
flexure),  and  is  continued  across  the  abdomen  as  the  transverse 
colon  until,  reaching  the  left  side,  it  curves  beneath  the  lower 
end  of  the  spleen  (left  colic  or  splenic  flexure),  and  passes  down- 
ward as  the  descending  colon.  Reaching  the  left  iliac  region  on 
a  level  with  the  margin  of  the  crest  of  the  ileum,  it  makes  a  curve 
like  the  letter  S,  —  hence  its  name  of  sigmoid  flexure,  —  and  finally 
ends  in  the  rectum.  (See  Fig.  166.) 

The  rectum.  —  The  rectum  is  from  six  to  eight  inches  (15  to 
20  cm.)  long;  it  passes  obliquely  from  the  left  until  it  reaches 
the  middle  of  the  sacrum,  then  it  follows  the  cui-ve  of  the  sacrum 
and  the  coccyx,  and  finally  arches  slightly  backward  to  its  ter- 
mination at  the  anus. 

The  anus  is  the  aperture  leading  from  the  rectum  to  the  exterior 
of  the  body.  It  is  guarded,  and  except  during  defecation  is  kept 
closed  by  the  contraction  of  two  involuntary  circular  muscles 
called,  respectively,  the  internal  and  external  sphincters. 

Coats  of  the  large  intestine.  —  The  large  intestine  has  the  usual 
four  coats  except  in  some  parts  where  the  serous  coat  only  par- 
tially covers  it,  and  the  rectum,  where  the  serous  coat  is  lacking. 
The  muscular  coat  consists  of  two  layers  of  fibres,  one  arranged 
longitudinally  and  the  other  circularly.  Beginning  at  the  appen- 
dix, the  longitudinal  fibres  are  arranged  in  three  ribbon-like  bands, 
which  extend  the  whole  length  of  the  colon  to  the  rectum,  and 
these  bands  being  shorter  than  the  rest  of  the  tube,  the  walls  are 
puckered  between  them.  The  third  coat  consists  of  submucous 
areolar  tissue,  and  the  fourth  or  inner  coat  consists  of  mucous 
u 


290  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 

membrane.     The  mucous  coat  possesses  no  villi  and  no  circular 
folds.     It  contains  numerous  tubular  glands  and  solitary  lymph 
nodules  which  closely  resemble  those  of  the  small  intestine. 
Functions.  —  The  functions  of  the  large  intestine  are  three. 

(1)  The  process  of  digestion  is  continued.     This  is  due  to  the  pres- 
ence of  bacteria,  and  to  the  digestive  fluids  with  which  the  food 
becomes  mixed  in  the  small  intestine.     (2)  The  process  of  absorp- 
tion is  continued,  and  (3)  the  waste  products  are  removed  from  the 
body. 

ACCESSORY  ORGANS  OF  DIGESTION 

The  accessory  organs  of  digestion  are :   (1)  the  salivary  glands, 

(2)  the  tongue,  (3)  the  teeth,  (4)  the  pancreas,  and  (5)  the  liver. 
The  first  three  have  been  described. 

-*        PANCREAS 

The  pancreas  is  an  elongated  organ,  of  a  pinkish  color,  which 
lies  in  front  of  the  first  and  second  lumbar  vertebrae  and  behind 
the  stomach.  It  weighs  between  two  and  three  ounces  (60  to 
90  grams),  is  about  six  inches  (15  cm.)  long,  two  inches  (5  cm.) 
wide,  and  one-half  inch  (1.25  cm.)  thick.  In  shape  it  somewhat 
resembles  a  hammer,  and  is  divided  into  head,  body,  and  tail. 
The  right  end,  or  head,  is  thicker  and  fills  the  curve  of  the  duode- 
num, to  which  it  is  firmly  attached.  The  left,  free  end  is  the  tail, 
and  reaches  to  the  spleen.  The  intervening  portion  is  the  body. 

Structure  of  the  pancreas.  —  It  is  a  compound  racemose  gland 
composed  of  lobules.  Each  lobule  consists  of  one  of  the  branches 
of  the  main  duct  which  terminates  in  a  cluster  of  saccules  that  are 
grape-like  in  appearance.  The  lobules  are  joined  together  by 
connective  tissue  to  form  lobes,  and  the  lobes,  united  in  the  same 
manner,  form  the  gland.  The  small  ducts  from  each  lobule  open 
into  one  main  duct  about  the  size  of  a  goose-quill,  which  runs 
lengthwise  through  the  gland,  from  the  tail  to  the  head.  The 
pancreatic  and  common  bile  duct  usually  enter  by  means  of  a 
common  opening  into  the  duodenum  about  three  inches  (7.5  cm.) 
below  the  pylorus.  Sometimes  the  pancreatic  duct  and  the  com- 
mon bile  duct  open  separately  into  the  duodenum,  and  there  is 
frequently  an  accessory  duct  which  opens  into  the  duodenum  about 
an  inch  above  the  orifice  of  the  main  duct.  (See  Fig.  174.) 


CHAP.  XIV]         THE  DIGESTIVE  SYSTEM 


291 


Islands  of  Langerhans .  —  Scattered  throughout  the  pancreas 
are  round  or  ovoid  bodies  known  as  the  islands  of  Langerhans, 
Each  island  is  about  one  twenty-fifth  inch  (1  mm.)  in  diameter  and 
consists  of  a  group  of  many-sided  cells.  They  are  surrounded  by 


COMMON    BILE  DUCT 


ORIFICE  OF 
ACCESSORY  - 
PANCREATIC  DUCT 


ORIFICE!  OF  BILB 
AND  PANCREATIC  DU.CTS 


SUP. 
M£SEtJTERIC  A.RTERY 


FIG.  174.  —  DUCTS  OF  THE  PANCREAS.     Part  of  the  front  wall  of  the  duodenum 
is  cut  away.     (Gerrish.) 

a  rich  capillary  network.  Their  function  is  to  furnish  the  internal 
secretion  of  the  pancreas. 

Function.  —  Two  secretions  are  formed  in  the  pancreas.  (1) 
The  pancreatic  fluid,  which  is  one  of  the  most  important  of  the 
digestive  fluids,  is  an  external  secretion  and  is  poured  into  the 
duodenum  during  intestinal  digestion.  (2)  The  secretion  formed 
by  the  islands  of  Langerhans  is  an  internal  secretion  that  is  ab- 
sorbed by  the  blood  and  carried  to  the  tissues.  This  internal 
secretion  aids  in  the  oxidation  of  glucose. 

Diabetes  mellitus.  —  This  is  a  disease  characterized  by  a  lack 
of  oxidation  of  glucose  and  its  consequent  loss  to  the  body  as  it 
is  excreted  in  the  urine.  ,The  cause  is  not  settled,  but  it  is  be- 


292 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 


lieved  that  disease  of  the  pancreas  involving  the  islands  of  Langer- 
hans  may  produce  this  condition.     (See  page  337.) 

THE   LIVER 

The  liver  (hepar)  is  the  largest  gland  in  the  body,  weighing 
ordinarily  from  fifty  to  sixty  ounces  (1500  to  1800  grams).  It 
measures  eight  to  nine  inches  (20  to  22  cm.)  from  side  to  side,  six 
to  seven  inches  (15  to  17.5  cm.)  from  front  to  back,  and  four  to 


FIG.   175.  —  THE  LIVER.     Front  view.     (Gerrish.) 

five  inches  (10  to  12  cm.)  from  above  downward  in  its  thickest  part. 
It  is  a  reddish  brown  organ,  placed  directly  below  the  diaphragm, 
in  front  of  the  right  kidney,  the  pyloric  end  of  the  stomach,  and 
the  upper  part  of  the  ascending  colon.  The  upper  convex  sur- 
face fits  closely  into  the  under  surface  of  the  diaphragm.  The 
under  concave  surface  of  the  organ  fits  over  the  right  kidney,  the 
upper  portion  of  the  ascending  colon,  and  the  pyloric  end  of  the 
stomach.  The  number  five  prevails  in  the  parts  and  appendages 
of  the  liver. 

Ligaments.  —  The  liver  is  connected  to  the  under  surface  of 
the  diaphragm,  and  the  anterior  walls  of  the  abdomen  by  five 
ligaments,  four  of  which  are  formed  by  folds  of  peritoneum,  and 


CHAP.  XIV]          THE   DIGESTIVE   SYSTEM 


293 


the  fifth,  or  round  ligament,  is  a  fibrous  cord  resulting  from  the 
atrophy  of  the  umbilical  vein  of  intra-uterine  life. 

Fissures.  —  The  liver  is  divided  by  five  fissures  into  five  lobes. 
The  important  fissures  are  (1)  the  portal,  or  transverse,  which 
is  the  gateway  for  vessels,  ducts,  and  nerves  to  enter  and  leave 


LOBg 


FIG.   176.  —  THE  LIVER.     Lower  surface.     (Gerrish.) 

the  liver,  and  (2)  the  gall-bladder  fissure,  which  supports  the  gall- 
bladder.    Both  these  fissures  are  in  the  under  surface  of  the  liver. 
Lobes.  —  The  liver  is  divided  into  five'  lobes  :  — 

1.  Right  (largest  lobe). 

2.  Left  (smaller  and  wedge-shaped). 

3.  Quadrate  (square). 

4.  Caudate  (tail-like). 

5.  Spigelian. 

Vessels.  —  The  liver  has  five  sets  of  vessels  :  — 

1.  Branches  of  portal  vein. 

2.  Hepatic  veins. 

3.  Bile  ducts. 

4.  Branches  of  hepatic  artery. 

5.  Lymphatics. 

Minute  anatomy  of  liver.  —  The  liver  may  be  regarded  as 
made  up  of  many  minute  livers  called  lobules.  Each  lobule  is  an 
irregular  body  from  one-twentieth  to  one-tenth  of  an  inch  (1-2 


294 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 


mm.)  in  diameter,  composed  of  a  multitude  of  hepatic  cells  packed 
so  closely  together  that  only  enough  room  is  left  between  them  for 
the  passage  of  blood-vessels,  ducts,  and  nerves.  Thus  each  lobule 
has  all  the  essentials  of  a  gland ;  (1)  blood-vessels  in  close  connec- 
tion with  secretory  cells,  (2)  cells  which  are  capable  of  forming  a 
secretion,  and  (3)  ducts  by  which  the  secretion  is  carried  away. 

The  portal  vein.  —  The  portal  vein  brings  to  the  liver  venous 
blood  from  the  stomach,  spleen,  pancreas,'  and  intestines.  After 
entering  the  liver,  it  divides  into  a  vast  number  of  branches 


INTERLOBULAR  VEIN 

INTERLOBULAR  DUCT 


HEPATIC  CELLS 


1NTRALOBULAR  VEIN 
A 

FIG.  177.  —  DIAGRAMMATIC  REPRESENTATION  OF  Two  HEPATIC  LOBULES. 
A  shows  the  interlobular  veins  running  around  the  outside  of  the  lobule  and  sending 
their  capillaries  into  the  lobule  to  join  the  central  vein.  In  B,  the  bile  capillaries 
are  seen  with  the  hepatic  cells  between  them,  the  bile  capillaries  radiating  to  the 
periphery  of  the  lobule,  where  they  join  the  interlobular  bile  ducts. 

which  form  a  network  surrounding  each  lobule,  and  hence 
are  known  as  interlobular  (between  the  lobules)  veins.  From  this 
network  minute  capillaries  enter  the  lobule,  penetrate  between 
each  cell  and  thus  surround  them,  so  that  each  cell  is 
generously  supplied  with  blood  containing  the  raw  material 
for  the  manufacture  of  bile.  These  capillary  branches  which 
enter  the  lobule  and  surround  the  cells  are  called  intralobular 
(within  the  lobule).  These  vessels  converge  toward  the  centre 
of  the  lobule  like  the  spokes  of  a  wheel  and  empty  into 
a  vein  (central)  which  carries  the  blood  away  from  the  lobule. 
The  central  veins  from  a  number  of  lobules  empty  into  a  much 
larger  vein  upon  whose  surface  a  vast  number  of  lobules  rest, 


CHAP.  XIV]         THE  DIGESTIVE  SYSTEM 


295 


and  therefore  the  name  sublobular  (under  the  lobule)  is  given  to 
these  veins.  They  empty  into  stili  larger  veins,  the  hepatic, 
which  converge  to  form  three  large  trunks  and  empty  into  the 
inferior  vena  cava,  which  is  embedded  in  the  posterior  surface  of 
the  gland. 

The  bile  ducts.  —  The  surfaces  of  the  hepatic  cells  are  grooved, 
and  the  grooves  on  two  adjacent  cells  fit  together  and  form  a 
channel  into  which  the  bile  is 
poured  as  soon  as  it  is  formed 
by  the  cells.  These  channels 
form  a  network  between  and 
around  the  cells  as  intricate  as 
the  network  of  blood-vessels. 
They  are  called  intralobular 
ducts,  and  empty  into  larger 
ducts  called  interlobular. 
These  unite  and  form  larger 
and  larger  ducts  until  two 
main  ducts,  one  from  the  right 
and  one  from  the  left  side  of 
the  liver,  unite  in  the  portal 
fissure  and  form  the  hepatic 
duct. 

The  hepatic  duct  runs  down- 
ward and  to  the  right  for  about  two  inches  (5  cm.)  and  then 
joins  at  an  acute  angle  the  duct  from  the  gall-bladder,  termed 
the  cystic  duct.  The  hepatic  and  cystic  ducts  together  form  the 
common  bile  duct  (ductus  communis  choledochus) ,  which  runs  down- 
ward for  about  three  inches  (7.5  cm.)  and  enters  the  duodenum 
about  three  inches  (7.5  cm.)  below  the  pylorus.  This  orifice 
usually  serves  as  a  common  opening  for  both  the  common  bile 
and  the  pancreatic  duct.  It  is  very  small  and  is  guarded  by  a 
sphincter  muscle  which  keeps  it  closed  except  during  digestion. 
(See  Fig.  174.) 

Hepatic  artery.  —  We  must  remember  that  the  blood  brought 
to  the  liver  by  the  portal  vein  is  venous  blood  and  is  not  intended 
for  purposes  of  nourishment  of  the  liver  itself,  hence  arterial  blood 
is  furnished  by  the  hepatic  artery.  It  enters  the  liver  with  the 
portal  vein,  divides  and  subdivides  in  the  same  manner  as  the 


FIG.  178.  —  LOBULE  OF  RABBIT'S 
LIVER,  VESSELS  AND  BILE  DUCTS  IN- 
JECTED, a,  central  or  intralobular  vein ; 
6,  6,  interlobular  veins ;  c,  interlobular 
bile  duct. 


296  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 

portal  veins,  thus  forming  another  network  between  the  lobules, 
and  in  the  lobules  between'  the  cells.  The  capillaries  from  the 
portal  vein  and  the  hepatic  artery  are  separate  and  distinct  until, 
near  the  centre  of  each  lobule,  they  unite,  and  all  the  blood  sup- 
plied to  the  liver  by  the  portal  vein  and  hepatic  artery  is  carried 
away  from  it  by  the  hepatic  veins  which  empty  into  the  inferior 
vena  cava. 

Lymphatics.  —  There  is  a  superficial  and  a  deep  set.  They 
begin  in  irregular  spaces  in  the  lobules,  form  networks  around 
the  lobules,  and  run  always  from  the  centre  outward.  They  drain 
off  waste  products  and  unconsumed  nutritious  substances. 

Glisson's  capsule.  —  The  whole  liver  is  invested  in  an  outer 
capsule  of  areolar  connective  tissue,  which  is  reflected  inward  at 
the  portal  fissure  and  encloses  the  vessels  and  ducts  passing 
through  this  opening. 

Serous  membrane.  —  With  the  exception  of  a  few  small  areas, 
the  liver  is  enclosed  in  a  serous  tunic  derived  from  the  peritoneum. 

Nerves.  —  Nerves  are  derived  from  the  left  vagus  and  the 
solar  plexus.1 

Functions.  —  The  liver  may  be  compared  to  a  wonderful 
laboratory,  the  most  wonderful  in  the  body.  It  has  three  im- 
portant functions :  — 

1 .  Bile  secreting.  —  The   cells   of  the   liver   manufacture   bile 
from  the  blood  brought  to  them  by  the  portal  vein.     The  function 
of  bile  is  considered  in  the  next  chapter. 

2.  Glycogenic.  —  The  cells   of  the   liver  take  from  the  blood 
brought  to  them  by  the  portal  vein  a  substance  called  glucose, 
which  is  derived  from  the  carbohydrates  of  our  food.     This  is 
stored  in  the  liver  in  the  form  of  glycogen  until  such  time  as  the 
body  needs  more  glucose  than  the  food  furnishes.     When  such 
demand  is  made,  the  liver  cells  reconvert  the  glycogen  into  glucose 
and  pour  it  into  the  circulation. 

3.  Higher  chemical  activities.  —  Many  of  the  end-products  of 
protein  digestion  cannot  be  eliminated  until  they  are  acted  upon 
by  the  liver,  and  changed  into  other  substances  which  the  kid- 
neys can  eliminate,  e.g.,  urea  is  made  from  some  of  these  end- 
products  brought  to  the  liver  by  the  blood.     It  is  probable  that  the 
liver  possesses  other  important  metabolic  functions  which  at  pres- 

1  See  page  401. 


CHAP.  XIV] 


SUMMARY 


297 


ent  are  not  fully  understood.  Some  physiologists  are  of  the  opinion 
that  fibrinogen  and  antithrombin  are  formed  in  the  liver. 

The  gall-bladder.  —  The  gall-bladder  is  a  pear-shaped  sac 
lodged  in  the  gall-bladder  fissure  on  the  under  surface  of  the  liver, 
where  it  is  held  in  place  by  connective  tissue.  It  is  about  four 
inches  (10  cm.)  long,  one  inch  (2.5  cm.)  wide,  and  holds  about 
ten  drachms  (40  cc.).  It  is  composed  of  three  coats  :  (1)  the  inner 
one  is  mucous  membrane,  (2)  the  middle  one  is  muscular  and  fibrous 
tissue,  and  (3)  the  outer  one  is  serous  membrane  derived  from  the 
peritoneum.  It  is  only  occasionally  that  the  peritoneum  covers 
more  than  the  under  surface  of  the  organ. 

Function.  —  The  gall-bladder  serves  as  a  reservoir  for  the  bile. 
During  digestion  the  bile  is  constantly  poured  into  the  intestine ; 
in  the  intervals  it  is  stored  in  the  gall-bladder. 


SUMMARY 

Digestion.  —  Digestion  is  dependent  on  the  proper  functioning  of  certain 
organs  that  are  grouped  together  and  called  the  digestive  system. 

Mouth. 
Pharynx. 

(Esophagus,  or  gullet. 
Stomach. 

Duodenum. 
Jejunum. 


Digestive 
System 


Alimentary 
Canal 


Alimentary 
canal 


Accessory 
organs 


Small  or  thin  in- 
testine 


Large  or  thick  in- 
testine 


Ileum. 
Caecum. 

Colon 
Rectum. 


Ascending. 

Transverse. 

Descending. 


Salivary  glands. 
Tongue. 
Teeth. 
Pancreas. 
Liver. 
Continuous  tube  from  mouth  to  anus. 


About  30  ft.  long. 
From  mouth  to   diaphragm  — 
3  coats 


From  diaphragm  to  rectum  — 
4  coats 


Mucous. 
Areolar. 
Muscular. 
Mucous. 
Areolar. 
Muscular. 
Serous    derived 
peritoneum. 


from 


298 


Mouth,  or 
Buccal  Cavity 


Tonsils 


Tongue 


Salivary 
Glands 


Teeth 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 
1.  Hard  palate. 


Above  —  palate 

Below  —  tongue. 
Front  —  lips. 
Sides  —  cheeks.  - 
Tonsils. 


2.  Soft  palate  —  uvula,  pillars  of  the 
fauces,  and  tonsils. 


Contains 


Tongue. 
Salivary  glands. 
Teeth. 


Collections  of  lymph  nodules  occupy  triangular  space 
between  pillars  of  the  fauces  on  either  side  of  throat. 

1.  May  be  a  source  of  lymphocytes  and  leu- 

cocytes. 

2.  May  act  as  a  filter  and  prevent  entrance  of 

microorganisms . 


Function 


Special  organ  of  sense  of  taste. 

1.  Stimulates  secretion  of  digestive  fluids. 

2.  Assists  in  swallowing. 

3.  Secretes  mucus. 


Assists    in 
digestion 


Parotid  —  just  under  and  in  front  of  ear. 

Submaxil-    "| 
lary          \  Below  the  jaw  and  under  the  tongue. 

Sublingual  J 

Function  —  Form  a  secretion,  that  mixed  with  the  secre- 
tion of  the  glandular  cells  of  the  mouth  is 
called  saliva. 

Contained  in  sockets  of  alveolar  processes  of  maxillae  and 

mandible. 

Gums  —  cover  processes  and  extend  into  sockets. 
Sockets  —  lined  with  perios-  f  Attaches  teeth  to  sockets. 

teum  1  Source  of  nourishment. 

f  Root  —  one   or   more   fangs   contained   in 
J      socket. 

1  Crown  —  projects  beyond  level  of  gums. 
[  Neck  —  portion  between  root  and  crown. 
Gives  shape. 

Encloses  pulp  cavity  which  con- 
tains nerves  and  blood-vessels, 
that  enter  by  canal  from  root. 
Enamel  —  Caps  the  crown. 
Cement  —  Covers  the  root. 


3  portions 

Composed 
of  three 
substances 
developed 
from  epi- 
thelium 


Dentine 


CHAP.  XIV] 


SUMMARY 


299 


Teeth 


2  sets 


1 .  Temporary  —       f  Incisors  8     } 
<  Canines  4 
I  Molars  8 
Incisors  8 
Canines  4 
Bicuspids  8 
Molars  12 
Function  —  To  assist  in  the  process  of  mastication. 


Temporary  — 
6  months  to 
2  yrs. 

Permanent  —  6| 
yrs.  to  21  yrs. 
of  age 


^20. 

J 


32. 


Pharynx 


'Cone-shaped  tube,  5  inches  long,  between  mouth  and 

oesophagus. 

Muscular,  lined  with  mucous  membrane. 
2  posterior  nares. 
2  Eustachian  tubes. 
7  apertures     1  fauces. 
1  larynx. 
.  1  oesophagus. 


(Esophagus, 
or  Gullet 


Tube  —  9  in.  long.     Extends  from  pharynx  to  stomach. 
Inner  —  mucous  —  disposed  in  folds. 
Middle  —  submucous. 

3  coats  (•  Internal  circular  layer. 

Outer  —  muscular  j  External    longitudinal 

I     layer. 

1.  Connects  the  pharynx  with  the  stomach. 
Function      ^  2.  Receives  the  food  and  passes  it  on  to 
stomach. 


Stomach,  or 
Gaster 


Dilated  portion  of  canal,  size  and  shape  vary. 

Oblique  position  in  epigastric  and  left  hypochondriac 

regions  under  the  diaphragm. 

Openings      j  Cardiac  orifice  —  connects  with  oesophagus. 
1  Pyloric  orifice  —  connects  with  duodenum. 


Curvatures 


Parts 


4  coats 


Lesser  curvature  —  concave  border. 
Greater  curvature  —  convex  border. 
Fundus  —  blind  end  to  the  left  of  the  heart. 
Intermediate  region  —  between  fundus  and 

pyloric  extremity. 
Pyloric  extremity  —  under  the  liver. 

1.  Outer  —  serous  —  peritoneum. 

[  1.  Longitudinal  layer. 

2.  Muscular  j  2.  Circular  layer. 

[  3.  Oblique  layer. 

3.  Submucous  —  vascular. 


300 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIV 


Stomach,  or 
Gaster 


4  coats 


Small,  or  Thin, 
Intestine 


4.  Mucous  < 


Glands 


Cardiac 


Peptic 


Rugae 

j  secrete 
I  mucus, 
chief  cells 
secrete  pep- 
sinogen  ; 
parieta 1 
cells  secrete 
acid. 

f  secrete 

Pyloric    Pepsino- 
I  gen     and 
(  mucus. 

j  Sympathetic  system. 
1  Vagi  nerves 
Blood-vessels  from  coeliac  axis. 

1.  Connects  the  oesophagus  with  the  intes- 

tine. 

2.  To   hold   the  food  while   it    undergoes 

gastric  digestion. 
I  3.  To  secrete  mucus  and  gastric  fluid. 
Convoluted  tube  extends  from  stomach  to  valve  of  colon. 
Twenty  feet,  coiled  up  in  abdominal  cavity. 

f  Duodenum. 
3  divisions  <  Jejunum. 
I  Ileum. 

1 .  Serous  from  peritoneum,  called  mesentery. 

2.  Muscular     {  Longitudinal  layer. 

I  Circular  layer. 

{Blood-vessels. 
Lymphatics. 
Nerves. 
4.  Mucous        1  V*lvula3  conniventes. 

i  Villi  —  contain  lacteals. 
Simple  follicles  ] 


Nerves 


Functions 


4  coats 


Glands 
and  nodes 


Duodenal  or 
Brunner's 


Lymph  nodules 


?  Secrete  intestinal  fluid. 

Solitary. 

Aggregated  lymph  nod- 
ules of  Peyer  —  fifty 
or  more  solitary  lymph 
nodules  form  so-called 
patches  in  small  in- 
testine. 


Function 


{Digestion. 
Absorption. 
Secretion  of  succus  entericus. 


CHAP.  XIV] 


SUMMARY 


301 


Large,  or 
Thick, 
Intestine 


Pancreas 


Largeness  in  width,  not  in  length. 
Length,  5  ft. ;  width,  2^  in.  to  \\  in. 
Extends  from  ileum  to  anus. 

CaBCum,  with  vermiform  appendix. 
Ascending. 
Transverse. 

Descending  with  sigmoid 
flexure. 

Internal  sphincter. 
External  sphincter. 

1.  Serous,  except  that  in  some  parts  it  is 
only  a  partial  covering,  and  at  rectum 
it  is  wanting. 


3  divisions 


4  coats 


Colon 


Rectum  —  anus 


2.  Muscular  - 


f  Arranged  in  three 
Longitu-  I  ribbon-like 
bands  that  be- 
gin at  appen- 
dix, and  extend 
to  rectum. 


dinal 
layer 


Circular 
layer 

3.  Submucous. 

No  villi. 

No  valvulae  conniventes. 

4.  Mucous    {  i  Tubular  glands. 

Numerous  j  Solitary    lymph 

[      nodules. 

f  Continuance  of  digestion  and  absorption. 
I  Elimination  of  waste. 
In  front  of  first  and  second  lumbar  vertebrae,  behind 
stomach. 

Head  attached  to  duodenum. 
Body  in  front  of  vertebra. 
Tail  reaches  to  spleen. 
Six  inchss  long. 
Two  inches  wide. 
One-half  inch  thick. 
Weight  —  two  to  three  ounces. 

Compound    gland  —  sacculated    ends    of 

tubules  form  lobules. 

Lobules  held  together  by  connective  tissue 
Structure     {      form  lobes. 

Lobes  form  gland. 

Duct  from  each  lobule  empties  into  pan- 
creatic duct. 


Function 


Hammer 
shape 

Size 


Function 


1.  Secretes  pancreatic  fluid. 

2.  Forms  an  internal  secretion. 


302 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XI? 


Liver 


Five        fis- 
sures 


Formed  by  folds  of  peri- 
toneum. 


Results  from  atrophy  of 
umbilical  vein. 


Under  surface. 


Dorsal  surface. 


Largest  gland  in  body. 

Right  hypochondriac. 
Location         Epigastric. 

Left  hypochondriac. 
Convex  above  —  fits  under  diaphragm. 
Concave  below  —  fits  over  right  kidney,  ascending  colon, 
and  pyloric  end  of  stomach. 
1.  Suspensory, 
broad,    or 
falciform 

Five     liga-  I  2.  Coronary 
ments       |  3.  Right  lateral 

4.  Left  lateral 

5.  Round      liga- 

ment 

1.  Umbilical    fis- 

sure 

2.  Gall-bladder 

fissure 

3.  Portal  or  trans- 

verse fissure 

4.  Ductus  venous 

fissure 

5.  Vena  cava 

1.  Right  (largest  lobe). 

2.  Left  (smaller  and  wedge-shaped). 

3.  Quadrate  (square). 

4.  Caudate  (tail-like). 

5.  Spigelian. 

f  1.  Branches  of  portal  vein. 

2.  Bile  ducts. 

3.  Hepatic  veins. 

4.  Branches  of  hepatic  artery. 

5.  Lymphatics. 

Hepatic  cells  jsW  in.  in  diameter  grouped 

in  lobules. 
Lobules  is  in.  in  diameter. 

Interlobular   veins    (be- 
tween lobules). 
Intralobular     capillaries 

(within  lobules). 
Branches  of  por-    Central  veins. 

tal  vein  I  Sublobular  veins  (under 

lobules) . 

Hepatic  veins  —  exit  at 
portal  fissure,  empty 
into  inferior  vena  cava. 


Five  lobes 


Five 
sets  of 
vessels 


Anatomy 
of  liver 


CHAP.  XIV] 


SUMMARY 


303 


Liver 


Gall-bladder 


Anatomy 
of  liver 


Functions 


Bile  ducts 


Branches  of  he- 
patic artery 


Lymphatics 


{ Channels  between  cells 

(within  lobules). 
Intralobular  -ducts. 
Interlobular  ducts. 
Hepatic  duct  —  exit  at 

portal  fissure. 
Interlobular         arteries 

(between  lobules). 
Intralobular     capillaries 

(within  lobules). 
Course  beyond  the  in- 
tralobular  capillaries 
same  as  that  pursued 
by  blood  from  portal 
vein. 

Start    in   lobules,    form 
network,  and  run  from 
centre  to  periphery. 
Act  as  drain-pipes. 
Glisson's  capsule  encloses  the  whole  of  the 

liver. 

Serous    membrane    from    the    peritoneum 
almost  completely  covers  it. 

1.  Bile  secreting. 

2.  Glycogenic. 

Changes  toxic  substances 
so  that  they  are  less 
harmful  and  more 
easily  eliminated,  e.g., 
urea. 

Pear-shaped  sac  lodged  in  gall-bladder  fissure  on  under 
surface  of  liver. 

f  Four  inches  long. 

\  One  inch  wide. 

[  Capacity  about  ten  drachms. 

!1.  Mucous  membrane. 
2.  Fibrous  and  muscular  tissue. 
3.  Serous  membrane  from  peritoneum. 
Function  —  Serves  as  a  reservoir  for  bile. 


Higher  chem- 
ical activities 


Size 


3  coats 


CHAPTER  XV 

FOOD.  —  DIGESTIVE  PROCESSES;  CHANGES  THE  FOOD  UNDER- 
GOES IN  THE  MOUTH,  STOMACH,  SMALL  AND  LARGE  INTES- 
TINES;  ABSORPTION 

THE  process  of  digestion  takes  place  in  the  alimentary  canal 
and  the  purpose  of  it  is  to  prepare  food  for  absorption 
and  utilization  by  the  tissues  of  the  body.  It  includes  not  only 
the  physical  process  of  changing  the  food  to  a  solution  or  emul- 
sion, but  also  the  chemical  process  of  cleavage,  i.e.,  the  splitting  of 
large  and  complex  molecules  into  smaller  and  simpler  ones.  Both 
these  processes  favor  diffusion.  Of  equal  significance  is  the 
standardization  of  food.  Digestion  obliterates  many  of  the  char- 
acteristics which  differentiate  foods  and  gives  us  at  last  much 
the  same  set  of  products,  whatever  the  meal  may  have  been.  From 
the  large  number  of  complex  compounds  taken  into  the  stomach, 
only  a  small  number  of  simple  substances  are  contributed  by  the 
intestines  to  the  blood.  It  is  also  a  process  of  refining  as  it  sepa- 
rates the  useful  from  the  useless  residue  of  our  food. 

FOOD 

Definition.  —  Food  is  any  substance  taken  into  the  body,  (1) 
to  provide  material  for  the  growth  of  body  tissues,  (2)  to  repair 
tissue  waste,  and  (3)  to  supply  heat  and  other  kinds  of  energy. 

After  birth  the  material  for  the  growth  of  the  body  is  derived 
from  our  food ;  also  the  material  to  make  good  the  loss  resulting 
from  the  daily  wear  and  tear  of  body  tissues.  All  the  body  ac- 
tivities require  a  certain  amount  of  energy ;  this  and  all  the  heat 
dissipated  from  the  body  must  be  supplied  by  food.  The  energy 
in  our  food  is  present  in  the  form  of  potential  or  latent  energy, 
binding  the  atoms  into  molecules,  and  the  molecules  into  larger 
masses.  The  splitting  of  these  complex  molecules  into  smaller 
and  simpler  ones  releases  energy.  Food  material,  over  and  above 

304 


CHAP.  XV]  FOOD  305 

what  is  needed  for  this  purpose,  is  stored  in  the  body  either  in  the 
form  of  fat,  or  as  glycogen  in  the  liver  and  muscles.  This  may  be 
regarded  as  so  much  reserve  fuel  which  is  oxidized  when  needed  to 
furnish  energy. 

Classification  of  food.  —  Chemical  analysis  shows  that  the 
elements l  found  in  the  body  are  also  found  in  food.  Various 
combinations  of  these  elements  give  us  a  great  variety  of  com- 
pound substances  which  are  divided  into  two  great  classes  of 
nutrients.  This  division  is  based  on  the  presence  or  absence  of 
carbon.  Those  which  contain  carbon  are  organic,  those  which  do 
not  are  inorganic.  These  are  further  subdivided  as  follows :  — 


Nutrients 

or 
Food  Principles 


1.  Inorganic 


2.  Organic 


f  Water. 

Mineral  matter  or  salts. 
Carbohydrates. 
Fats. 
Proteins. 


Water.  —  Water  (H2O)  is  a  very  stable  compound  of  hydrogen 
and  oxygen.  It  enters  into  the  composition  of  all  the  tissues, 
supplies  fluid  for  the  body,  acts  as  a  solvent  for  food,  and  aids  in 
the  elimination  of  waste.  Next  to  air  it  is  the  most  necessary  prin- 
ciple of  life  and  constitutes  about  two-thirds  of  the  body  weight 
(66  per  cent). 

Salts.  —  The  principal  inorganic  salts  are  :  — 


Chloride 
Phosphate 
Sulphate 
Carbonate 


of  sodium  and  potassium. 


Phosphate  ]     „      ,  . 

\  of  calcium  and  magnesium. 
Carbonate  J 

The  inorganic  salts  are  an  essential  part  of  all  the  tissues,  and  take 
part  in  the  functions  of  the  body  in  six  ways :  (1)  they  maintain 
the  alkaline  or  neutral  reaction  of  the  fluids  of  the  body ;  (2)  they 
furnish  the  material  for  the  acidity  or  alkalinity  of  the  digestive 
fluids  and  other  secretions ;  (3)  they  help  in  regulating  the  flow  of 
fluids  to  and  from  the  tissues,  because  they  maintain  the  normal 
osmotic  pressure;  (4)  they  enter  largely  into  the  composition  of 
the  bones,  teeth,  and  cartilage ;  (5)  they  are  necessary  for  the 

1  See  page  5. 


306 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  XV 


clotting  of  blood  ;  and  (6)  they  give  the  fluids  of  the  body  their 
influence  upon  the  elasticity  and  irritability  of  nerve  and  muscle. 
Carbohydrates.  —  All  sugars  and  starches  are  grouped  under 
the  name  of  carbohydrates.  They  contain  but  three  ele- 
ments, carbon,  hydrogen,  and  oxygen,  the  two  latter  in  the  pro- 
portion to  form  water.  The  varieties  of  carbohydrates  are  as 

follows  :  — 

Glucose  or  dextrose,  found  in  fruits,  es- 
pecially the   grape,   and   in   the   blood. 


Simple  or  Mono- 
saccharids 


Fructose  or  levulose,  found  with  glucose  in 
fruits.     C6Hi206. 


Invert 
sugar. 


Simple  sugars.  —  Simple  sugars  are  one  of  the  standard  sub- 
stances which  the  tissues  can  use,  and  as  they  are  freely  soluble 
and  of  small  molecule  they  are  readily  absorbed. 


Complex  or 
Disaccharids 


f  Sucrose  or  cane  sugar.  Ci2H22Oii. 
|  Lactose  or  milk  sugar.  Ci2H22Oii. 
[  Maltose  or  malt  sugar.  Ci2H22On. 


Complex  sugars.  —  A  study  of  the  formulas  of  the  complex 
sugars  will  show  that  the  composition  is  the  same  but  they  are 
differently  named  because  they  give  different  reactions.  Before 
any  of  the  complex  sugars  can  be  utilized  in  the  body  they  must 
first  be  changed  either  into  glucose,  or  into  invert  sugar,  which 
consists  of  a  molecule  each  of  glucose  and  fructose.  Only  one 
splitting  is  necessary  as  one  molecule  of  a  complex  sugar  plus  one 
molecule  of  water  will  form  one  molecule  of  glucose  and  fructose. 

COMPLEX  SUGAR      WATER  GLUCOSE         FRUCTOSE 

+  H20  =  C6H1206 .  C6H1206 


Poly  saccharids 


Invert  Sugar 

Starch  —  found  in  grain,  tubers,  roots,  etc. 
Cellulose  —  outside     covering     of     starch 

grains,     and     basis     of     all 

woody  fibres. 
Glycogen  —  form  in  which  sugar  is  stored 

in  the  liver  and  muscles. 
Dextrin  —  formed  from  starch  by  partial 

hydrolysis. 


(C6H1005)n 


(C6H1005)n 
(C6H1006)n 


(C6H1005)n 


Poly  saccharids.  —  In  all  of  these  compounds  the  composition 
of  the  molecule  is  supposed  to  be  rather  complex,  although  the 


CHAP.  XV]  FOOD  307 

elements  are  present  in  the  same  relative  proportion,  as  shown 
in  the  formulae.  The  value  of  n,  however,  may  be  very 
small  or  very  large  and  is  probably  different  for  each  polysaccha- 
rid,  which  makes  the  actual  composition  of  each  member  of  the 
group  different.  For  instance,  n  for  the  starch  molecule  is  large, 
while  for  the  dextrin  molecule  it  is  smaller,  so  that  a  single  starch 
molecule  in  digestion  may  split  into  several  molecules  of  dextrin  of 
the  same  relative  composition.  In  the  disaccharids  only  one 
splitting  is  necessary,  as  each  molecule  of  a  complex  sugar  plus 
one  molecule  of  water  will  give  two  molecules  of  a  simple 
sugar.  As  poly sacchar ids  are  so  complex,  they  must  pass 
through  several  stages  before  they  are  changed  by  hydrolytic 
cleavage  to  a  simple  sugar.  Each  splitting  of  the  molecule 
gives  substances  with  simpler  composition,  though  with  the 
same  relative  proportion  of  the  constituents,  and  to  each  is 
given  a  special  name.  Thus  as  the  result  of  the  first  splitting  we 
have  dextrin,  of  which  there  are  three  varieties,  i.e.,  erythrodextrin, 
achroodextrin,  and  maltodextrin,  each  one  being  produced  as  a 
result  of  the  further  splitting  of  the  molecules;  then  maltose,  a 
disaccharid,  is  yielded,  and  finally  glucose,  a  monosaccharid  or 
simple  sugar.  The  number  of  molecules  of  simple  sugar  resulting 
from  the  hydrolysis  of  any  polysaccharid  would  depend  upon  the 
value  of  n. 

Fats.  —  Fats  are  composed  of  carbon,  hydrogen,  and  oxygen, 
but  the  hydrogen  content  is  relatively  high.  The  ordinary  fats 
of  animal  and  vegetable  food  are  not  simple  substances,  but  are 
mixtures  of  simple  fats  named  palmitin,  stearin,  and  olein,  which 
are  derived  from  the  fatty  acids,  palmitic,  stearic,  and  oleic.  Each 
molecule  of  a  simple  fat  is  made  from  one  molecule  of  glycerine 
and  three  molecules  of  a  fatty  acid.  This  reaction  is  comparable 
to  the  neutralization  of  an  acid  by  a  base  resulting  in  a  salt  and 

water.     (See  page  8.) 

•!.<£-   -^%V 

Acid  -f    Base   ->•  Salt  +  Water 
HC1  +  NaOH  ->•  NaCl  +   H2O 

Acid  +       Base       -»-  Salt  +  Water 

(STEARIC  ACID)  (GLYCERINE)  (STEARIN)  (WATER) 

3  H  •  Ci8H3502  +  C3H5(OH)3  •*•  C3H5(C18H35O2)3  +  3  H2O 


308  ANATOMY  AND   PHYSIOLOGY       [CHAP.  XV 

In  general,  fats  and  oils  are  practically  the  same,  and  the  mixture 
of  fats  found  in  the  body  is  liquid  at  the  body  temperature.  They 
are  soluble  in  ether,  chloroform,  and  hot  alcohol,  but  are  insoluble 
in  water.  Under  the  influence  of  steam,  mineral  acids,  and  cer- 
tain enzymes  found  in  the  body,  fats  split  up  into  the  substances 
of  which  they  are  built,  i.e.,  glycerine  and  fatty  acids.  Accord- 
ingly, the  digestion  of  fats  is  a  reaction  in  exactly  the  opposite  di- 
rection from  the  one  above. 

Salt  +  Water  ->-       Base        +         Acid 

(STEARIN)  (WATER)  (GLYCERINE)  (STEARIC  ACID) 

2)3  +  3  H20  ->-  C3H5(OH)3  +  3  H.Ci8H35O2 


The  process  of  saponification  is  similar  to  the  above,  only  that 
instead  of  water  a  base  is  used  and  the  final  products  are  glycerine 
and  soap. 

Salt          +         Base       ->•      Base        +          Soap 

(POTASSIUM 
(STEARIN)  HYDROXIDE)  (GLYCERINE)  (SOAP) 

C3H6(Ci8H3502)3  +       3  KOH     ->•  C3H5(OH)3  +  3  K(C18H35O2). 

Proteins.  —  Proteins  consist  of  carbon,  hydrogen,  nitrogen, 
oxygen  ;  sulphur,  phosphorus,  and  other  elements  may  be  present. 
They  are  more  complex  than  either  carbohydrates  or  fats  and  dif- 
fer from  them  in  having  nitrogen,  hence  they  are  described  as  nitrog- 
enous compounds.  Proteins  are  difficult  to  analyze  but  modern 
chemists  have  shown  that  they  are  built  up  of  simpler  substances 
called  amino-acids.  Accordingly,  the  digestion  of  proteins  which 
is  a  process  of  hydrolysis  means  reducing  them  to  amino-acids, 
and  the  number  of  stages  through  which  they  pass  depends  upon 
the  size  1  and  the  complexity  of  the  molecule.  Each  splitting  of  the 
molecule  gives  substances  with  simpler  composition  and  to 
each  such  substance  is  given  a  special  name,  i.e.,  ->•  Protein 
-»-Metaprotein->-Proteo3es->-  Peptones  ->•  Peptids  ->•  Amino-acids. 
The  number  of  molecules  of  amino-acids  resulting  from  the  hy- 
drolysis of  any  protein  would  depend  upon  the  size  of  the  molecule. 

About  twenty  amino-acids  have  been  described,  and  are  some- 
times compared  to  the  letters  of  the  alphabet.  Various  com- 
binations of  letters  result  in  an  enormous  number  of  words.  In  a 
similar  way  various  combinations  of  amino-acids  result  in  many 

1  The  large  size  of  the  protein  molecule  can  be  judged  by  the  empirical  formula 
assigned  to  globin,  one  of  the  simplest  forms: 


CHAP.  XV] 


FOOD 


309 


Simple 


Conjugated 


Proteins 


different  kinds  of  proteins  which  give  different  reactions  and  are 
represented  by  different  formulae. 

Classification  of  proteins.  —  For  experimental  purposes  proteins 
have  been  classified  as  shown  below;  the  classification  being 
based  on  their  solubility  in  various  reagents  and  on  other  reactions. 

Albumins. 

Globulins. 

Glutelins. 

Alcohol-soluble  proteins  (prolamines). 

Albuminoids. 

Histons. 

Protamins. 

Nucleoproteins. 

Glycoproteins. 

Phosphoproteins. 

Haemoglobins. 

Lecithoproteins. 

Primary          derivatives  1 

(formed    through    hy- 

drolytic  changes  which 

cause   only   slight   al- 
terations of  the  protein 

molecule) 
Secondary       derivatives 

(products    of    further 

hydrolytic  cleavage  of 

the  protein  molecule) 

In  this  classification  the  group  called  simple  proteins  hydrolyze 
to  amino-acids,  conjugated  proteins  yield  amino-acids  and  some 
other  body.  This  latter  substance  is  nuclein  in  the  nucleoproteins, 
a  carbohydrate  in  the  glycoproteins,  a  phospho  body  in  the  phos- 
phoproteins,  hsematin  in  haemoglobins,  and  a  fatty  substance  in 
lecithoproteins.  The  derived  proteins  are  changed  forms  produced 
by  the  action  of  heat,  acids,  alkalies,  or  enzymes. 

Accessory  articles  of  diet.  —  In  addition  to  the  foodstuffs 
proper,  our  foods  contain  numerous  other  substances  which  in 
one  way  or  another  are  useful  in  nutrition,  although  not  absolutely 
necessary.  These  substances,  differing  in  nature  and  importance, 
may  be  classified  under  the  three  heads  of :  — 

Flavors :    The  various  oils  or  esters  that  give  odor  and  taste  to  foods. 
Condiments  :     Salt,  pepper,  mustard,  etc. 
Stimulants :    Tea,  coffee,  cocoa,  meat  extracts,  etc. 


Derived 


Proteans. 
Metaproteins. 
Coagulated  proteins. 


Proteoses. 
Peptones. 
Peptids. 


310  ANATOMY  AND  PHYSIOLOGY       [CHAP.  XV 

DIGESTIVE  PROCESSES 

In  a  broad  sense  all  the  processes  by  which  foods  are  rendered 
available  to  an  organism  are  digestive  processes.  The  word 
alimentation  is  often  used  to  include  the  preparatory  processes 
together  with  the  digestive  processes.  In  this  sense,  many  indus- 
trial and  domestic  processes  are  in  line  with  digestion  and  often 
initiate  the  task  which  the  digestive  organs  complete.  This  is 
particularly  true  of  cooking,  for  by  it  various  chemical  changes  are 
brought  to  pass ;  such,  for  example,  as  changing  starches  into  dex- 
trins,  partially  splitting  fats  into  glycerine  and  fatty  acids,  and 
changing  some  proteins  to  the  first  stages  of  their  decomposition 
products.  A  second  reason  for  classifying  cooking  as  a  digestive 
process  is  that  the  appearance,  odor,  and  taste  of  food  are  im- 
proved, and  these  facts  stimulate  the  end  organs  of  the  special 
senses,  causing  a  reflex  stimulation  of  the  digestive  mechanisms. 
In  a  third  way  cooking  may  profoundly  aid  digestion  by  killing 
parasites  or  bacteria  which  otherwise  would  gain  a  foothold  in  the 
alimentary  canal  and  thus  modify  or  change  digestive  processes. 
It  is  usual  to  describe  digestion  within  the  body  as  consisting  of 
two  processes,  i.e.,  mechanical  and  chemical. 

Both  the  mechanical  and  chemical  processes  of  digestion  are 
controlled  by  the  nervous  system.  Any  severe  strain  or  strong 
emotion  which 'affects  the  nervous  system  unpleasantly,  inhibits 
the  secretion  of  the  digestive  fluids  and  interferes  with  digestion, 
often  checking  the  appetite  and  even  preventing  the  taking  of 
food.  On  the  other  hand,  pleasurable  sensations  aid  digestion, 
hence  the  value  of  attractively  served  food,  pleasant  surroundings, 
and  cheerful  conversation. 

Mechanical  digestion.  —  Mechanical  digestion  is  effected  by 
various  physical  processes  that  occur  in  the  alimentary  canal.  It 
is  to  be  considered  as  preliminary  to  the  more  important  chemical 
digestion.  It  serves  four  important  purposes  :  (1)  in  taking  food 
in  and  moving  it  along  through  the  alimentary  canal  just  rapidly 
enough  to  allow  the  required  chemical  changes  to  take  place  in 
each  part;  (2)  in  lubricating  the  food  by  adding  the  mucin  and 
water  secreted  by  the  glands  of  the  alimentary  canal ;  (3)  in  lique- 
fying the  food  by  mixing  it  with  the  various  digestive  fluids ;  and 
(4)  in  separating  the  food  into  small  particles,  thereby  increasing 


CHAP.  XV]  DIGESTIVE  PROCESSES  311 

the   amount   of  surface  to  come  in  contact  with  the  digestive 
fluids. 

The  mechanical  processes  consist  of  :  — 

1.  Mastication. 

2.  Deglutition  or  swallowing. 

3.  Peristaltic  action  of  oesophagus. 

4.  Movements  of  the  stomach. 

5.  Movements  of  the  intestines. 

6.  Defecation. 

Chemical  digestion.  —  The  most  essential  part  of  digestion 
is  chemical  and  is  a  process  of  hydrolytic  cleavage  which  is  de- 
pendent upon  the  presence  of  enzymes.  The  term  hydrolysis 
means  the  breaking  down  of  complex,  molecules  into  simpler  ones 
with  the  absorption  of  water.  An  example  of  hydrolysis  is  the 
conversion  of  any  of  the  complex  sugars  into  simpler  sugars. 
(See  page  306.) 

Necessity  for  chemical  digestion.  —  Chemical  digestion  is  neces- 
sary because  organic  foods,  with  the  exception  of  simple  sugars, 
cannot  diffuse  through  animal  membranes,  and  even  if  diffusion 
were  possible,  the  tissues  could  not  use  them,  hence  they  must  be 
reduced  to  smaller  molecules  and  to  such  standard  substances  as 
the  tissues  can  use,  i.e.,  (1)  simple  sugars,  resulting  from  the 
digestion  of  all  carbohydrate  foods ;  (2)  glycerine  and  fatty  acids, 
resulting  from  the  digestion  of  fats ;  and  (3)  amino-acids,  result- 
ing from  the  digestion  of  proteins. 

Cause  of  chemical  digestion.  —  It  is  possible  to  make  carbo- 
hydrates, fats,  and  proteins  undergo  the  same  changes  outside  the 
body  as  occur  during  digestion.  Carbohydrates,  fats,  and  pro- 
teins, if  boiled  with  a  mineral  acid  or  subjected  to  the  action  of 
enzymes,  will  hydrolyze  and  split  up  into  simpler  substances. 
Within  the  body  these  changes  take  place  at  body  temperature, 
and  are  due  to  the  enzymes  present  in  all  of  the  digestive  fluids. 

Enzymes.  —  The  exact  composition  of  enzymes  is  not  known. 
One  author  suggests  the  following  definition  :  "  An  enzyme  is  a 
substance  produced  by  living  cells  which  acts  by  catalysis."  In 
other  words,  they  are  organic  substances  which  vary  (hasten  or 
retard)  the  speed  of  reactions,  but  do  not  initiate  them.  Their 
efficacy  is  destroyed  by  boiling.  The  following  characteristics 
may  be  noted  :  — 


312  ANATOMY  AND  PHYSIOLOGY       [CHAP.  XV 

Optimum  temperature.  —  The  body  enzymes  act  best  at  the 
temperature  of  the  body.  They  are  destroyed  by  a  high  tem- 
perature and  their  effect  is  retarded  wholly  or  in  part  by  a  low 
temperature. 

Medium.  —  Each  enzyme  requires  a  medium  of  definite  reaction 
either  acid,  alkaline,  or  neutral.  The  enzyme  of  saliva  requires  an 
alkaline  or  neutral  medium,  while  the  enzymes  of  the  gastric 
fluid  require  an  acid  medium. 

Active  and  inactive  form.  —  It  has  been  demonstrated  that  an 
enzyme  may  exist  within  the  cell  producing  it  in  an  antecedent  or 
inactive  form  which  is  designated  as  a  zymogen.  The  zymogen 
may  be  stored  in  the  cell  in  the  form  of  granules  which  are  con- 
verted into  active  enzyme  at  the  moment  of  secretion,  or  it  may  be 
secreted  in  inactive  form  and  require  the  cooperation  of  some  other 
substance  before  it  is  capable  of  effecting  its  normal  reaction. 
In  such  cases  the  second  substance  is  said  to  activate  the  enzyme. 
An  example  is  found  in  the  case  of  the  enterokinase  which  acti- 
vates the  trypsinogen  of  the  pancreatic  secretion.  (See  page  321.) 

Coenzymes.  —  There  are  some  cases  where  the  action  of  an 
enzyme  is  helped  by,  or  even  dependent  upon  the  presence  of  some 
other  substance.  A  good  example  of  this  activity  is  furnished  by 
the  influence  of  bile-salts  upon  lipase.1  These  cases  of  coactivity 
are  to  be  distinguished  from  activation,  by  the  fact  that  the 
combination  may  be  made  or  unmade.  For  example,  in  a  mixture 
of  bile  salts  and  lipase,  the  bile  salts  may  be  removed  by  dialysis. 
In  activation,  on  the  contrary,  the  active  enzyme  cannot  be 
changed  back  to  the  inactive  zymogen. 

Classification  of  enzymes.  —  There  is  no  consensus  of  opinion 
among  physiologists  or  chemists  as  to  the  system  to  be  followed  in 
naming  or  classifying  enzymes.  Recently  it  has  been  suggested 
that  an  enzyme  be  designated  by  the  name  of  the  substance  on 
which  it  acts,  and  that  all  of  them  be  given  the  termination  ase. 
According  to  this  system  the  enzyme  acting  on  starch  would  be 
amylase ;  that  on  maltose,  maltase ;  that  on  fat,  lipase.  This 
suggestion  has  been  followed  in  part  only,  as  the  older  enzymes  are 
still  most  frequently  referred  to  under  their  original  names.  The 
following  classification  is  a  modification  from  a  standard  physiol- 
ogy: 2  - 

1  See  page  322.  2  Howell's  "  Text-book  of  Physiology,"  sixth  edition. 


CHAP.  XV]  DIGESTIVE  PROCESSES  313 

1.  The    sugar-splitting   enzymes.     These    fall    into    two    subgroups: 
(a)  The  inverting  enzymes,  which  convert  the  double  sugars  or  disac- 
charids   into   the   monosaccharids.     Examples:     Maltase,    which   splits 
maltose  to  dextrose;  invertase,  which  splits  cane-sugar  to  dextrose  and 
levulose;  and  lactase,  which  splits  milk-sugar  (lactose)  to  dextrose  and 
galactose.     (6)  The  enzymes,  which  split  the  monosaccharids.     There 
is  evidence  of  the  presence  in  the  tissues  of  an  enzyme  capable  of  splitting 
the  sugar  of  the  blood  and  tissues  (glucose)  into  lactic  acid. 

2.  The  amylolytic  or  starch-splitting  enzymes.     Examples:   Ptyalin 
or  salivary  •  diastase,   amylase,   or  pancreatic   diastase.     They  cause  a 
hydrolytic  cleavage  of  the  starch  molecule. 

3.  The   lipolytic,    or   fat-splitting   enzymes.     Example:    The   lipase 
found  in  the  pancreatic  secretion,  in  the  liver,  connective  tissues,  blood, 
etc.     They  cause  a  hydrolytic  cleavage  of  the  fat  molecule. 

4.  The  proteolytic  or  protein-splitting  enzymes.     Examples :   Pepsin 
of  gastric  fluid,  trypsin  of  pancreatic  fluid.     They  cause  a  hydrolytic 
cleavage  of  the  protein  molecule. 

5.  The  clotting  enzymes,  which  convert  soluble  to  insoluble  proteins. 
Example  :     The  clotting  of  the  casein  of  milk  by  rennin. 

6.  The  oxidizing  enzymes,  or  oxidases.     A  group  of  enzymes  which  set 
up  oxidation  processes.     Opinions  differ  in  regard  to  the  manner"  in  which 
these  enzymes  act. 

7.  The  deaminizing  enzymes.     All  amino-acids  contain  an  NH2  group 
which  is  split  off  by  hydrolytic  cleavage  and  is  converted  to  ammonia  —> 
NH3,  and  then  probably  to  urea  ->-  NH2— CO— NH2.    See  page  339. 


CHANGES  THE  FOOD  UNDERGOES  IN  THE  MOUTH 

Mastication. — When  solid  food  is  taken -into  the  mouth  it  is 
cut  and  ground  by  the  teeth,  being  pushed  between  them  again 
and  again  by  the  muscular  contractions  of  the  cheeks,  and  the 
movements  of  the  tongue,  until  the  whole  is  thoroughly  crushed 
and  ground  down,  thus  exposing  a  larger  surface  to  the  action  of 
the  digestive  fluids. 

Insalivation.  —  During  the  process  of  mastication  saliva  is 
poured  in  large  quantities  into  the  mouth,  and  mixing  with  the 
food,  lubricates,  moistens,  and  reduces  it  to  a  soft,  pulpy  condi- 
tion. A  certain  amount  of  air  caught  in  the  bubbles  of  the  saliva 
also  becomes  entangled  in  the  food,  and  this  facilitates  the  pene- 
tration of  the  gastric  fluid. 

Secretion  of  saliva.  —  The  secretion  of  saliva  is  the  result  of 
reflex  stimulation  of  the  nerves  connected  with  the  salivary  glands. 
This  is  a  psychical  reflex  which  is  initiated  by  the  sight,  thought,  or 


314  ANATOMY  AND  PHYSIOLOGY       [CHAP.  XV 

smell  of  food,  acting  as  stimulants  to  the  sensory  or  afferent  nerves 
which  carry  these  impulses  to  a  nerve  centre  in  the  brain  (prob- 
ably in  the  medulla  oblongata),  and  from  thence  motor  impulses 
are  transmitted  through  efferent  nerves  to  the  gland.  The  move- 
ments of  mastication  and  the  taste  of  food  continue  this  stimu- 
lation, so  that  the  secretion  is  continued  till  the  end  of  the  meal. 

Saliva.  —  Saliva  is  a  mixture  of  the  secretions  of  all  three  pairs 
of  salivary  glands,  as  well  as  of  the  small  glands  of  the  mucous 
membrane  of  the  mouth.  It  consists  of  water,  some  mucin,  and 
an  enzyme  called  ptyalin  or  salivary  diastase.  It  has  a  specific 
gravity  of  1 .004  to  1 .008  and  an  alkaline  reaction  when  tested  with 
litmus  paper.  The  amount  secreted  in  twenty-four  hours  is 
estimated  to  be  from  one  to  two  quarts  (1-2  litres). 

The  functions  of  saliva.  —  Saliva  has  four  distinct  functions : 
(1)  by  softening  and  moistening  the  food  it  assists  in  mastication 
and  deglutition ;  (2)  by  coating  the  food  with  mucin  it  lubricates 
it  and  insures  a  smooth  passage  along  the  oesophagus ;  (3)  by  dis- 
solving dry  and  solid  food  it  provides  a  necessary  step  in  the  pro- 
cess of  stimulating  the  taste  nerves,  and  taste  sensations  play  an 
important  part  in  the  secretion  of  gastric  fluid ;  (4)  by  virtue  of 
the  enzyme  which  it  contains  it  changes  starch  to  simpler  sub- 
stances, i.e.,  dextrin  and  maltose. 

Ptyalin  or  salivary  diastase.  —  By  the  action  of  the  enzyme 
ptyalin  which  is  present  in  saliva,  starch  is  partially  changed  to 
dextrin  and  maltose.  This  process  is  a  complicated  one  con- 
sisting of  a  series  of  hydrolytic  changes  which  take  place  in  suc- 
cessive stages,  and  result  in  a  number  of  intermediate  compounds. 
The  change  is  best  effected  at  the  temperature  of  the  body,1  in  a 
slightly  alkaline  solution,  saliva  that  is  distinctly  acid  hindering 
or  arresting  the  process.  Boiled  starch  is  changed  more  rapidly 
and  completely  than  raw,  but  food  is  rarely  retained  in  the  mouth 
long  enough  for  the  saliva  to  more  than  begin  the  transformation 
of  starch. 

Deglutition  or  swallowing.  —  The  softened  and  moistened  food 
is  brought  together  on  the  upper  surface  of  the  tongue  and  pressed 
backward  through  the  fauces  into  the  pharynx.  Then  the  muscu- 
lar bands  in  the  wall  of  the  pharynx  contract  and  force  the  food  into 

1  A  temperature  of  100°  F.  in  the  alimentary  canal  is  necessary  for  digestion, 
hence  iced  drinks  or  iced  foods  that  lower  this  temperature  delay  digestion. 


CHAP.  XV]  DIGESTIVE  PROCESSES  315 

the  oesophagus.  At  this  moment  breathing  has  to  be  suspended 
and  the  passages  closed  against  the  possible  entrance  of  food.  The 
soft  palate  is  drawn  back,  thus  protecting  the  nasal  passages,  and 
the  larynx  is  shielded  by  being  pulled  forward  under  the  root  of 
the  tongue,  and  has  an  additional  safeguard  through  the  folding 
down  upon  it  of  the  epiglottis.  When  food  is  once  within  the 
oesophagus;  breathing  may  be  resumed  and  the  downward  passage 
of  the  food  is  assisted  by  the  peristaltic  action  of  the  oesophagus. 

When  liquids  are  swallowed  they  are  shot  down  the  oesophagus 
by  the  initial  act  of  swallowing,  and  may  find  the  cardiac  orifice 
closed.  In  this  case,  the  liquid  is  held  until  the  peristaltic  wave 
reaches  the  cardiac  orifice,  when  the  tissues  relax  and  allow  the 
liquid  to  pass. 

Peristalsis.  —  Peristalsis  occurs  in  such  tubular  viscera  as  the 
oesophagus,  stomach,  intestines,  etc.,  which  possess  muscular 
coats.  Peristalsis  consists  of  a  series  of  wave-like  contractions 
of  the  circular  fibres  which  affect  successive  portions  of  the  tube 
from  above  downward.  The  constricted  portion  is  always  pre- 
ceded by  an  area  of  relaxation,  which  renders  the  contraction  more 
effective  in  forcing  the  contents  onward.  The  direction  is  always 
the  same,  and  the  action  is  under  the  control  of  the  nervous  system. 

Summary.  —  During  the  process  of  mastication,  insalivation, 
and  deglutition  the  food  is  first  reduced  to  a  soft,  pulpy  condition ; 
second,  any  starch  it  may  contain  begins  to  be  changed  into  sugar ; 
third,  it  acquires  a  more  or  less  alkaline  reaction. 

Vomiting.  —  Under  ordinary  circumstances  the  contractions  of 
the  cardiac  sphincter  muscle  prevent  the  regurgitation  of  food,  but 
strong  contractions  of  the  stomach  or  spasmodic  contractions  of 
the  abdominal  muscles  may,  if  the  diaphragm  is  fixed,  force  the 
contents  of  the  stomach  through  the  oesophagus  and  mouth  to  the 
exterior.  This  is  called  vomiting. 

\CHANGES  THE  FOOD  UNDERGOES  IN  THE  STOMACH,  OR 
STOMACH   DIGESTION 

The  food  which  enters  the  stomach  is  delayed  there  by  the 
contraction  of  the  sphincter  muscles  at  the  cardiac  and  pyloric 
openings.  The  cavity  of  the  stomach  is  always  the  size  of  its 
contents,  which  means  that  when  it  is  empty  it  is  contracted,  but 
when  food  enters,  it  expands  just  enough  to  hold  it.  Within  a 


316  ANATOMY  AND   PHYSIOLOGY       [CHAP.  XV 

few  minutes  after  the  entrance  of  food  small  contractions  start 
in  the  middle  region  of  the  stomach  and  run  toward  the  pylorus. 
These  contractions  are  regular  and  become  more  and  more  forcible 
as  digestion  progresses.  As  a  result  of  these  movements  the  food 
is  macerated,  mixed  with  the  acid  gastric  fluid,  and  reduced  to  a 
thin  liquid  mass  called  chyme.  At  certain  intervals  the  pyloric 
sphincter  relaxes  and  the  wave  of  contraction  forces  some  of  the 
chyme  into  the  duodenum.  The  fundal  end  of  the  stomach  does 
not  take  part  in  these  movements,  but  serves  as  a  reservoir  for 
food  which  is  under  slight  pressure,  as  the  muscles  are  in  a  state 
of  continual  contraction  or  tone.  Due  to  the  lack  of  movement 
and  the  muscular  tone,  the  gastric  fluid  cannot  penetrate  the  bolus 
of  food,  and  the  ptyalin  with  which  it  became  mixed  in  the  mouth 
continues  its  action,  and  the  digestion  of  starch  continues  for  about 
half  an  hour.  As  the  chyme  is  gradually  forced  into  the  duodenum, 
the  pressure  of  the  fundus  forces  the  food  into  the  pyloric  end. 

The  stomach  is  admirably  adapted  to  receive  a  large  amount 
of  food  within  a  short  period  of  time.  It  reduces  this  food  to 
chyme,  and  at  intervals  charges  the  intestine  with  small  amounts 
of  this  chyme  in  such  condition  as  to  admit  of  rapid  digestion.  It 
seems  probable  that  without  the  stomach,  our  mode  of  eating  would 
have  to  be  changed,  as  it  would  not  be  possible  to  load  the  intes- 
tine with  the  amount  of  food  ordinarily  consumed  at  a  meal. 

Time  required  for  stomach  digestion.  —  It  is  obvious  that  the 
time  required  for  gastric  digestion  depends  upon  the  nature  of  the 
food  eaten.  An  average  meal  of  mixed  food  requires  about  five 
hours  for  gastric  digestion.  The  ejection  of  chyme  through  the 
pylorus  occurs  at  regular  intervals,  and  is  supposed  to  depend 
upon  the  consistency  and  acidity  of  the  chyme.  Solid  particles 
forced  against  the  pylorus  tend  to  keep  it  closed,  but  hydrochloric  ify/ 
acid  in  the  stomach  seems  to  favor  or  produce  relaxation  of  ther/ 
pyloric  sphincter.  In  the  intestines  hydrochloric  acid  has  a  con- 
trary effect,  as  it  causes  a  contraction  of  the  sphincter,  which 
remains  closed  after  each  ejection  until  the  acidity  has  been 
neutralized. 

Secretion  of  gastric  fluid.  —  The  secretion  of  gastric  fluid 
seems  to  begin  in  advance  of  the  actual  arrival  of  food  in  the 
stomach,  and  to  be  in  proportion  to  the  pleasure  of  the  meal.  It 
continues  as  long  as  food  remains  in  the  stomach,  and  is  caused 


CHAP.  XV]  DIGESTIVE   PROCESSES  317 

and  maintained  by  two  factors :  (1)  psychical,  the  sensations  of 
eating ;  the  taste  and  odor  of  food  stimulate  the  sensory  nerves 
situated  in  the  mouth  and  nose.  These  afferent  impulses  are 
transferred  through  nerve  centres  to  efferent  fibres  of  the  vagus 
nerve,  and  thus  are  carried  to  the  stomach.  (2)  Chemical,  (a) 
by  secretogogues  contained  in  certain  foods  and  (6)  by  secreto- 
gogues  contained  in  the  products  of  digestion.  Certain  foods, 
such  as  meat  juices  and  extracts,  contain  substances  called  secreto- 
gogues or  hormones  which  are  supposed  to  act  directly  upon  the 
nerves  of  the  pyloric  mucous  membrane  and  form  a  substance 
called  gastrin  or  gastric  secretin,  which  is  absorbed  into  the  blood 
and  carried  to  the  gastric  glands.  This  substance  stimulates  the 
glands  to  secretion.  Other  foods,  such  as  milk,  bread,  white  of 
egg,  etc.,  do  not  appear  to  contain  secretogogues.  When  such 
foods  are  eaten,  a  psychical  secretion  is  started  and  when  this  has 
acted,  some  products  of  their  digestion  in  turn  become  capable 
of  stimulating  a  further  secretion  of  gastric  fluid. 

Gastric  fluid.  —  Gastric  fluid  is  secreted  by  the  gastric  glands 1 
lining  the  mucous  membrane  of  the  stomach.  It  is  a  thin, 
colorless,  or  nearly  colorless  liquid  with  a  strong  acid  re- 
action, and  a  specific  gravity  of  about  1.002-1.003.  The  quan- 
tity secreted  depends  upon  the  amount  of  food  to  be  digested. 
Upon  analysis  it  is  found  to  contain  some  protein,  some  mucin, 
and  inorganic  salts,  but  the  essential  constituents  are  hydro- 
chloric acid  and  two  or  possibly  three  enzymes,  pepsin,  rennin, 
and  lipase. 

Hydrochloric  acid.  —  It  is  generally  believed  that  the  parietal 
cells  of  the  gastric  glands  secrete  the  hydrochloric  acid,  from 
chlorides  found  in  the  blood.  The  chief  chloride  is  sodium  chloride 
(NaCl),  and  by  some  means  this  is  decomposed ;  the  chlorine  (Cl) 
combines  with  hydrogen  (H),  and  is  then  secreted  upon  the  free 
surface  of  the  stomach  as  hydrochloric  acid  (HC1).  In  normal 
gastric  fluid  it  is  found  in  the  proportion  of  0.2  to  0.4  per  cent. 
It  serves  (1)  to  activate  pepsinogen  and  convert  it  to  pepsin ;  (2) 
provides  an  acid  medium  which  is  necessary  for  the  pepsin  to 
carry  on  its  work ;  (3)  swells  the  protein  fibres,  thus  giving  easier 
access  to  pepsin ;  (4)  it  helps  in  the  inversion  of  sugar,  i.e.,  chang- 
ing complex  sugars  to  simple  ones ;  (5)  it  acts  as  a  disinfectant 

1  See  page  282. 


318  ANATOMY  AND   PHYSIOLOGY       [CHAP.  XV 

and  kills  many  bacteria  that  enter  the  stomach,  and  (6)  it  helps 
to  regulate  the  opening  and  closing  of  the  pyloric  valve. 

Pepsin.  —  Pepsin  is  supposed  to  be  formed  in  the  pyloric 
glands  and  the  chief  cells  of  the  gastric  glands.  It  is  present  in 
these  cells  in  the  form  of  a  zymogen,  an  antecedent  inactive  sub- 
stance called  pepsinogen  which  is  quickly  changed  to  active  pep- 
sin by  the  action  of  hydrochloric  acid. 

Pepsin  is  a  weak  proteolytic  enzyme  requiring  an  acid  medium 
in  which  to  work.  It  has  the  property  of  converting  more  or  less 
of  the  protein  of  the  food  into  simpler  and  more  soluble  proteoses 
and  peptones.  This  action  is  preparatory  to  the  more  complete 
hydrolysis  that  takes  place  in  the  intestines  under  the  influence  of 
trypsin  and  erepsin,  for  peptones  are  not  absorbed  but  suffer  a 
further  hydrolysis  to  amino-acids. 

Rennin.  —  Rennin,  like  pepsin,  is  supposed  to  be  formed  in  the 
chief  cells  of  the  gastric  glands  in  a  zymogen  form,  the  prorennin 
which  after  secretion  is  converted  to  the  active  enzyme.  So  far 
as  is  known,  this  enzyme  acts  only  upon  the  soluble  protein  of 
milk,  which  is  called  caseinogen.  It  converts  this  substance  into 
a  clotted  mass  called  curd ;  the  digestion  of  which  is  carried  on 
by  the  pepsin,  and  later  in  the  intestine  by  the  trypsin. 

Various  observers  have  described  other  enzymes  in  addition  to 
the  pepsin  and  rennin,  but  the  evidence  regarding  these  is  uncer- 
tain. It  is  probable  that  the  ptyalin  swallowed  with  the  food 
continues  the  digestion  of  starchy  material  in  the  fundus  for  some 
time.  Regarding  the  fats,  it  is  believed  that  they  undergo  no 
true  digestive  change  in  the  stomach.  They  are  set  free  from  their 
mixture  with  other  foodstuffs  by  the  dissolving  action  of  the  gas- 
tric fluid;  they  are  liquefied  by  the  heat  of  the  body,  and  are 
scattered  through  the  chyme  in  a  coarse  emulsion  by  the  move- 
ments of  the  stomach,  all  of  which  favors  the  subsequent  action 
of  the  pancreatic  fluid.  Emulsified  fats  like  cream  are  acted  upon 
to  a  limited  extent  by  a  third  enzyme  called  gastric  lipase,  and  this 
action  may  be  important  in  the  digestion  of  milk  fat  by  infants, 
as  the  pancreas  is  inactive. 

Summary.  —  The  stomach  serves  as  a  place  for  storage  and 
maintains  a  gradual  delivery  to  the  intestine.  The  movements 
are  adapted  to  promote  the  mechanical  reduction  of  food.  Sali- 
vary digestion  of  starch  continues  until  the  acidity  is  everywhere 


CHAP.  XV]  DIGESTIVE   PROCESSES  319 

established.     Gastric  digestion  affects  proteins  chiefly  and  is  in- 
complete.    There  is  some  digestion  of  emulsified  fat. 


CHANGES  THE  FOOD  UNDERGOES  IN  THE  SMALL 
INTESTINE 

The  chyme,  entering  the  duodenum,  after  an  ordinary  meal,  is  a 
mixture  of  various  matters.  It  probably  contains  proteoses  and 
peptones  derived  from  the  proteins ;  dextrins  and  sugar  from  the 
carbohydrates ;  traces  of  glycerine  and  fatty  acids  from  the  fats ; 
portions  of  all  the  foods  not  yet  digested ;  hydrochloric  acid  from 
the  gastric  fluid ;  and  lactic  acid  produced  by  fermentation.  It  is 
in  the  intestines  that  this  mixture  undergoes  the  most  profound 
digestive  changes.  These  changes  which  constitute  intestinal 
digestion  are  effected  by :  (1)  the  movements  of  the  intestines, 
(2)  the  pancreatic  fluid,  (3)  the  succus  entericus  or  secretion  of  the 
intestinal  glands,  and  (4)  the  bile. 

Movements  of  the  small  intestine. — The  movements  of  the 
small  intestine  are  of  two  kinds :  (1)  peristaltic  and  (2)  pendular 
or  rhythmic  segmentation. 

(1)  A  peristaltic  movement  may  be  defined  as  a  quick  succes- 
sion of  waves  of  contraction  and  inhibition  passing  slowly  along 
the  intestine.     The  wave  of  contraction  begins  at  a  certain  point, 
passes  downward  away  from  the  stomach,  and  is  always  pre- 
ceded by  an  area  of  inhibition  or  relaxation.     The  purpose  of  it  is 
to  pass  the  food  slowly  forward,  and  it  is  obvious  that  the  wave 
of  contraction  is  more  effective  in  forcing  the  contents  forward 
because  just  in  front  of  it  the  intestine  is  relaxed. 

(2)  The  movements  of  pendular  or  rhythmic  segmentation  con- 
sist of  local  constrictions  of  the  intestinal  wall  which  occur  rhyth- 
mically at  points  where  masses  of  food  lie.     The  purpose  of  these 
constrictions  is  to  divide  the  string  of  food  into  a  number  of  equal 
segments.     Within  a  few  seconds  each  of  these  segments  is  halved 
and  the  corresponding  halves  of  adjoining  segments  unite.     Again 
constrictions  recur  and  these  newly  formed  segments  are  divided, 
and  the  halves  reform  in  the  same  position  as  they  had  at  first. 
In  this  way  every  particle  of  food  is  brought  into  intimate  contact 
with  the  valvulse  conniventes  and  is  thoroughly  mixed  with  the 
digestive  fluids. 


320  ANATOMY  AND  PHYSIOLOGY        [CHAP.  XV 

Secretion  of  pancreatic  fluid.  —  Just  as  the  chewing  and  swallow- 
ing of  food  starts  the  gastric  secretion,  so  the  presence  of  acid  chyme 
in  the  intestine  starts  the  pancreatic  secretion.  This  effect  is 
due  to  a  special  substance  called  secretin  which  is  formed  by  the 
action  of  the  acid  upon  a  substance  called  prosecretin  which  is 
present  in  the  mucous  membrane  of  the  intestine.  This  secretin 
is  absorbed  by  the  blood  and  carried  to  the  pancreas,  which  it 
stimulates  to  activity.  (See  page  322.) 

Pancreatic  fluid.  —  Healthy  pancreatic  fluid  is  a  clear,  some- 
what viscid  fluid,  with  a  very  decided  alkaline  reaction.  The 
amount  secreted  in  twenty-four  hours  is  about  one  to  one  and  two- 
thirds  pints  (500  to  800  cc.).  It  contains  few  solids  and  is  depen- 
dent for  its  remarkable  power  on  three  enzymes :  (1)  trypsin,  (2) 
pancreatic  diastase  (amylase),  and  (3)  lipase  (steapsin).  Some 
authors  state  that  the  secretion  contains  a  fourth  enzyme,  i.e., 
rennin. 

Action  of  pancreatic  fluid  upon  food.  —  Pancreatic  fluid  has  the 
power  of  acting  on  all  the  foodstuffs,  proteins,  carbohydrates,  and 
fats.  This  action  is  due  to  its  enzymes. 

(1)  Trypsin.  —  Trypsin  is  secreted  in  the  form  of  a  zymogen 
called  trypsinogen,  and  is  activated  by  enterokinase,  an  enzyme 
which  is  contained  in  the  mucous  membrane  of  the  small  intestine. 
Trypsin,  like  pepsin,  causes  hydrolytic  cleavage  of  proteins,  but 
the  action  is  more  rapid  and  powerful,  and  the  protein  mole- 
cule is  broken  up  into  simpler  substances  than  peptones,  depending 
on  the  amount  of  trypsin  and  the  time  that  it  acts.     If  complete 
hydrolysis  takes  place,  the  end-products  consist  chiefly  of  amino- 
acids.     Trypsin    attacks   proteins   in    slightly   acid,    neutral,    or 
strongly  alkaline  mediums.     The  preliminary  action  of  pepsin,  on 
a  protein  molecule,  hastens  the  action  of  trypsin,  and  renders  it 
more  complete  than  if  the  trypsin  acted  alone. 

(2)  Diastase  (Amylase) .  —  The  action  of  diastase  is  similar  to 
that  of  ptyalin.     It  causes  hydrolysis  of  starch  with  the  production 
of  achroodextrin  and  maltose.    The  starchy  food  that  escapes  diges- 
tion in  the  mouth  and  stomach  becomes  mixed  with  this  enzyme 
and  continues  under  its  action  until  the  ileo-caecal  valve  is  reached. 
Before  absorption,  achroodextrin  and  maltose  are  further  acted 
upon  by  the  maltase  of  the  intestinal  secretion  and  converted  to 
dextrose. 


CHAP.  XV]  DIGESTIVE   PROCESSES  321 

(3)  Lipase  (Steapsin) .  —  Lipase  is  an  enzyme  capable  of  hy- 
drolyzing  fats  to  glycerine  and  fatty  acids.  The  process  of  hydroly- 
sis is  preceded  by  the  mechanical  process  of  emulsification  which 
results  in  tiny  droplets  of  fat.  This  increases  the  surface  of  fat  ex- 
posed to  the  chemical  action  of  the  lipase  and  from  a  physiological 
standpoint  is  regarded  as  a  preparatory  process.  Glycerine  and 
fatty  acids  are  absorbed  by  the  epithelium  of  the  intestine,  and 
again  combine  to  form  fat.  It  is  probable  that  in  this  synthesis 
the  fatty  acids  combine  with  the  glycerine  in  such  proportions 
as  to  make  the  kind  of  fat  characteristic  of  the  animal.  The 
action  of  lipase  is  said  to  be  reversible,  i.e.,  it  causes  both  the 
splitting  of  the  fats  and  the  synthesis  of  the  split  products,  not  only 
in  the  intestines,  but  in  the  various  tissues,  during  the  metabolism 
or  the  storage  of  fat.  Lipase  is  found  in  blood  and  in  many  tis- 
sues, —  muscle,  liver,  mammary  glands,  etc. 

There  is  a  possibility  that  the  fat  (salt)  may  combine  with  an 
alkali  (base)  and  form  soap.  This  reaction  is  known  as  saponifica- 
tion.  It  is  difficult  to  say  how  far  it  usually  goes  on. 

Succus  entericus,  or  intestinal  fluid.  —  Succus  entericus  is  the 
secretion  of  the  intestinal  glands.  It  is  a  clear,  yellowish  fluid, 
having  a  marked  alkaline  reaction  and  containing  a  certain  quan- 
tity of  mucin.  There  is  much  disagreement  as  to  the  properties 
and  importance  of  this  secretion.  It  is  said  to  have  little  or 
no  digestive  action  except  upon  starches ;  nevertheless,  the  general 
tendency  is  to  attribute  to  it,  plus  the  intracellular  enzymes,  a 
larger  share  in  the  work  of  digestion  than  was  formerly  granted. 
These  intracellular  or  endo-enzymes  are  not  secreted  into  the  lumen 
of  the  intestine  but  are  held  within  the  cells,  and  strictly  speaking, 
are  not  a  constituent  of  the  intestinal  fluid.  However,  it  is  their 
action  on  food  that  is  the  important  contribution  of  the  intestinal 
glands  to  digestion.  These  enzymes  and  their  actions  are  as 
follows :  — 

Enterokinase.  —  This  enzyme  activates  the  trypsinogen  of  pan- 
creatic fluid  and  converts  it  into  trypsin. 

Erepsin.  —  This  enzyme  hydrolyzes  proteoses  and  peptones  to 
amino-acids,  thus  completing  the  work  begun  by  the  pepsin  and 
trypsin.  It  is  claimed  that  it  occurs  not  only  in  the  intestinal 
mucosa  but  also  in  the  liver,  kidney,  pancreas,  and  possibly  in 
other  tissues. 


322  ANATOMY  AND  PHYSIOLOGY       [CHAP.  XV 

Inverting  enzymes.  —  These  enzymes  are  three  in  number  and 
convert  disaccharids  into  monosaccharids. 

1.  Maltase   acts   upon   the  products  formed  in  the  digestion 
of   starches,  i.e.,  dextrin   and   maltose,    and    converts   them   to 
dextrose. 

2.  Invertase  or  sucrase  acts  upon  sucrose  and  changes  it  to 
dextrose  and  levulose. 

3.  Lactase  acts  upon  lactose  and  changes  it  to  dextrose  and 
galactose. 

This  inverting  action  is  necessary  because  double  sugars  cannot 
be  used  by  the  tissues  and  would  escape  in  the  urine,  but  in  the 
form  of  simple  sugars  they  are  readily  used  by  the  tissues. 

Secretin.  —  This  is  not  an  enzyme,  but  a  hormone,  and  plays 
an  important  part  in  the  control  of  the  secretion  of  the  pancreas. 
It  is  secreted  or  formed  in  the  intestinal  mucosa  in  a  preliminary 
form  called  prosecretin,  and  under  the  influence  of  acid  is  changed 
to  secretin.  Secretin  is  absorbed  and  carried  to  the  pancreas, 
which  it  stimulates  to  activity. 

Bile.  —  Bile  is  a  fluid  of  a  golden  brown  or  greenish  color l 
with  an  alkaline  reaction.  It  is  secreted  continuously  by  the 
liver,  but  only  enters  the  duodenum  during  the  period  of  digestion. 
During  the  intervening  period  it  is  prevented  from  entering  the 
duodenum  by  the  sphincter  which  closes  the'  common  bile  duct, 
and  consequently  backs  up  into  the  gall-bladder.  Apparently  the 
ejection  of  chyme  into  the  duodenum  excites  a  contraction  of  the 
gall-bladder  and  an  inhibition  of  the  sphincter  which  results  in 
an  ejection  of  bile.  The  quantity  secreted  in  twenty-four  hours 
varies  with  the  amount  of  food  taken,  but  is  estimated  at  about 
one  to  one  and  two-thirds  pints  (500  to  800  cc.).  Bile  contains  no 
enzymes,  but  serves  as  a  coenzyme  and  activates  the  lipase  of  the 
pancreatic  fluid.  Its  physiological  effects  may  be  grouped  as 
follows :  — 

1.  Digestive  secretion.  —  It  serves  as  a  digestive  secretion  by 
accelerating  the  action  of  the  lipase  of  the  pancreatic  fluid  in 
splitting  fats  to  glycerine  and  fatty  acids,  and  aids  in  the  absorption 
of  these  products. 

2.  Excretion.  —  Its  value  as  an  excretion  we  know  little  about, 

1  The  color  of  bile  is  determined  by  the  respective  amounts  of  the  bile  pigments : 
(1)  biliverdin,  and  (2)  bilirubin,  that  are  present. 


CHAP.  XV]  DIGESTIVE  PROCESSES  323 

but  it  is  thought  to  serve  as  a  channel  by  which  the  products  of 
the  disintegration  of  haemoglobin  are  carried  from  the  body. 

3.  Antiseptic.  —  It  has  a  feeble  and  questioned  antiseptic  action 
upon  the  intestinal  contents,  and  its  presence  limits  putrefaction 
to  some  extent. 

Action  of  bacteria  in  small  intestine.  —  Numerous  bacteria 
which  are  able  to  hydrolyze  carbohydrates  and  proteins  are  con- 
stantly present  in  the  small  intestine.  Fermentation  of  the  car- 
bohydrates gives  rise  to  organic  acids,  such  as  lactic  and  acetic, 
but  none  of  the  products  of  this  fermentation  are  considered  toxic. 
On  the  other  hand,  the  putrefaction  of  proteins  gives  rise  to  a  num- 
ber of  end-products  that  are  distinctly  toxic.  Under  normal  con- 
ditions and  on  a  mixed  diet,  carbohydrate  fermentation  is  the  char- 
acteristic action  of  the  bacteria  in  the  small  intestine ;  while  protein 
putrefaction  occurs  in  the  large  intestine.  The  reason  for  this  seems 
to  be  that  carbohydrates  serve  to  protect  proteins  because  some  of 
the  bacteria  of  the  small  intestine,  i.e.,  bacillus  coli,  will  not  at- 
tack proteins  as  long  as  carbohydrate  material  is  present.  In 
addition,  the  organic  acids  produced  by  the  fermentation  of  car- 
bohydrates tend  to  neutralize  the  alkalinity  of  the  intestinal 
secretion,  and  may  even  give  an  acid  reaction.  An  acid  reaction 
is  unfavorable  to  the  action  of  the  bacteria  that  hydrolyze  proteins, 
and  in  this  way  putrefaction  in  the  small  intestine  is  prevented. 
From  this  it  follows  that  the  nature  of  bacterial  activity  in  the 
small  intestine  depends  upon  the  character  of  the  diet,  which  may 
be  intentionally  chosen  to  favor  one  or  the  other  kind. 

CHANGES  THE  FOOD  UNDERGOES  IN  THE  LARGE 
INTESTINE 

Movements  of  the  large  intestine. — After  the  food  passes 
from  the  small  intestine  into  the  large  intestine,  its  regurgitation 
is  prevented  by  the  closure  of  the  ileo-csecal  valve.  When  the 
caecum  becomes  filled,  strong  contractions  of  the  walls  exert  pres- 
sure upon  the  contained  food  and  force  it  into  the  ascending  colon. 
The  waves  of  contraction  which  pass  over  the  walls  of  the  ascend- 
ing colon  are  described  as  antiperistaltic  because  they  pass  in  two 
directions,  (1)  from  the  small  intestine,  and  (2)  toward  the  small 
intestine.  This  delays  the  food,  keeps  it  moving  backward  and 
forward,  and  helps  absorption.  It  has  been  estimated  that  it 


324  ANATOMY  AND  PHYSIOLOGY       [CHAP.  XV 

requires  about  two  hours  for  the  food  to  pass  from  the  ileo-csecal 
Valve  to  the  hepatic  flexure,  and  about  four  and  one-half  hours 
to  reach  the  splenic  flexure. 

Secretion  of  the  large  intestine.  —  The  secretion  of  the  large 
intestine  contains  much  mucin,  shows  an  alkaline  reaction,  and  is 
not  characterized  by  the  presence  of  enzymes.  When  the  con- 
tents of  the  small  intestine  pass  the  ileo-caecal  valve,  they  still 
contain  a  certain  amount  of  unabsorbed  food  material.  This  re- 
mains a  long  time  in  the  intestine,  and  since  it  contains  the  diges- 
tive enzymes  received  in  the  duodenum,  the  process  of  digestion 
and  absorption  continues. 

By  the  abstraction  of  all  the  soluble  constituents,  and  especially 
by  the  withdrawal  of  water,  the  liquid  contents  become,  as  they 
approach  the  rectum,  changed  into  a  firm  and  solid  mass  of  waste 
matters,  ready  for  ejection  from  the  body,  and  called  feces. 

Action  of  bacteria  in  large  intestine.  —  Protein  putrefaction 
due  to  the  action  of  bacteria  is  a  constant  and  normal  occurrence 
in  the  large  intestine.  The  reaction  is  alkaline,  and  whatever  pro- 
tein may  have  escaped  digestion  and  absorption  is  acted  upon  by 
the  bacteria  and  undergoes  putrefactive  fermentation.  The' split- 
ting of  the  protein  molecule  by  this  process  is  very  complete,  and 
the  end-products  differ  from  those  resulting  from  the  hydrolysis 
caused  by  acids  or  enzymes.  The  list  of  end-products  of  putre- 
faction is  a  long  one.  Some  are  given  off  in  the  feces,  others  are 
absorbed  and  later  excreted  in  the  urine.  The  action  of  bacteria 
is  considered  of  doubtful  value.  It  is  possible  that  they  may  act 
upon  the  cellulose  of  vegetable  foods  and  render  it  useful  in  nu- 
trition. A  conservative  view  is  that  bacteria  confer  no  positive 
benefit,  but  under  normal  conditions  the  body  is  able  to  neutralize 
their  injurious  action. 

The  feces. — The  feces  consist  of:  (1)  the  undigested  and 
indigestible  parts  of  the  food,  (2)  the  products  of  bacterial  de- 
composition, (3)  great  quantities  of  bacteria  of  different  kinds, 
(4)  bile  and  other  secretions,  (5)  enzymes,  and  (6)  inorganic  salts. 
Some  authorities  teach  that  a  certain  amount  of  indigestible  ma- 
terial in  the  diet  is  wholesome.  It  stimulates  the  lining  of  the 
intestines,  promotes  peristalsis,  and  as  it  is  pushed  along  the  tube 
takes  with  it  the  less  bulky  but  more  toxic  wastes.  The  color  of 
feces  is  due  to  the  presence  of  pigments  derived  from  the  bile. 


CHAP.  XV]  ABSORPTION  325 

Defecation.  —  The  anal  canal  is  guarded  by  an  internal  sphincter 
muscle  of  the  involuntary  type,  and  an  external  sphincter  that  is 
voluntary,  but  both  are  supplied  with  nerves  from  the  central 
nervous  system  and  consequently  defecation  is  a  voluntary  act. 
Normally  the  rectum  is  empty  until  just  before  defecation.  Various 
stimuli  (depending  on  one's  habits)  will  produce  peristaltic  action 
of  the  colon,  so  that  a  small  quantity  of  feces  enters  the  rectum. 
This  irritates  the  sensory  nerve-endings  and  causes  a  desire  to 
defecate.  The  voluntary  contraction  of  the  abdominal  muscles, 
the  descent  of  the  diaphragm,  and  powerful  peristalsis  of  the 
colon  all  combine  to  empty  the  colon  and  rectum. 

One  of  the  commonest  causes  of  constipation  is  the  retention  of 
feces  in  the  rectum  because  of  failure  to  act  on  the  desire  for  defe- 
cation. After  feces  once  enter  the  rectum  there  is  no  retroperi- 
stalsis  to  carry  it  back  to  the  colon,  and  the  sense  of  irritation  be- 
comes blunted.  The  desire  may  not  recur  for  twenty-four  hours, 
and  during  this  time  the  feces  continue  to  lose  water,  become 
harder,  and  more  difficult  to  expel. 

ABSORPTION 

This  is  the  process  by  means  of  which  the  digested  food  is  taken 
from  the  intestines  and  carried  into  the  blood.  We  have  now  to 
consider  this  process,  for,  properly  speaking,  though  the  food  may 
be  digested  and  ready  for  nutritive  purposes,  it  is  practically  out- 
side the  body,  until  it  passes  through  the  walls  of  the  alimentary 
canal. 

Absorption.  —  Absorption  is  a  very  complex  process  and  may 
be  subdivided  into  a  physical  and  a  physiological  process.  The 
physical  process  consists  in  the  passage  of  the  digested  food  from 
the  intestines  into  the  blood-vessels,  and  is  governed  by  the  laws 
of  diffusion  and  osmosis.  The  physiological  process  consists  in 
the  building  up  of  the  end-products  of  digestion  into  the  substances 
found  in  the  blood.  This  process  of  reconstruction  is  dependent 
on  the  living  epithelial  cells  that  make  up  the  intestinal  walls. 

Paths  of  absorption.  —  There  are  two  paths  by  means  of  which 
the  products  of  digestion  find  their  way  into  the  blood  :  — 

(1)  By  the  capillaries  in  the  walls  of  the  intestines. 

(2)  By  the  lymphatics  in  the  walls  of  the  small  intestine  (the 
lacteals) . 


326  ANATOMY  AND  PHYSIOLOGY       [CHAP.  XV 

There  is  reason  to  believe  that  but  little  absorption  occurs  in  the 
"  stomach.  It  is  now  thought  that  by  far  the  greater  part  of  ab- 
sorption is  a  function  of  the  small  intestine.  Normally,  the  valu- 
able part  of  the  digested  food  has  been  absorbed  before  the  colon 
is  reached,  but  it  is  true  that  the  colon  possesses  some  reserve  power 
of  absorption,  which  may  be  considered  supplementary  to  the 
absorption  occurring  in  the  small  intestine.  An  interesting  fea- 
ture is  the  marked  absorption  of  water.  In  the  small  intestine 
the  loss  of  water  due  to  absorption  is  made  good  by  osmosis  or 
secretion  of  water  into  the  intestine,  since  the  contents  at  the  ileo- 
csecal  valve  are  quite  as  fluid  as  at  the  pylorus.  In  the  large  in- 
testine water  is  absorbed  in  large  quantities  and  there  is  no  com- 
pensating secretion  to  offset  this  loss,  hence  the  contents  as  they 
approach  the  rectum  become  more  firm  and  solid. 


CHAP.  XVj 


SUMMARY 


327 


Digestion 


Food 


Classifica- 
tion 

Nutrients 

Inorganic 

or 

Food  Principles 

Organic 

Water 


Mineral 
Matter 


Carbohy- 
drates 


SUMMARY 

Physical  process  of  changing  food  to  a  solution  or  emulsion. 
Chemical  process  of  splitting  large  and  complex  molecules 

into  smaller  and  simpler  ones. 
Any  substance  taken  into  the  body  to 

1.  Provide  material  for  growth  of  tissues. 

2.  Provide  material  for  repair  of  tissue  waste. 

3.  To  supply  heat  and  other  kinds  of  energy. 

Chemical  analysis  shows  that  elements  found  in  body  are 
found  in  food.  Classification  based  on  presence  or  absence 
of  carbon. 

Water. 

Mineral  matter  or  salts. 

Carbohydrates. 

Fats. 

Proteins. 

H20.    About  66  per  cent  of  body  weight. 
Found  in  all  tissues. 
Supplies  fluid. 
Acts  as  solvent. 
Aids  in  elimination  of  waste. 
Chloride 
Phosphate 
Sulphate 
Carbonate 


Phosphate 
Carbonate 


of  sodium  and  potassium. 


of  calcium  and  magnesium. 

1.  To  maintain  alkaline  or  neutral  reaction  of 

body  fluids. 

2.  To  furnish  material  for  acidity  or  alkalinity 

of  digestive  fluids. 
Functions  \  3.  To  maintain  osmotic  pressure. 

4.  To  enter  into  bones,  teeth,  and  cartilage. 

5.  To  assist  in  the  clotting  of  blood. 

6.  To    influence    elasticity    and    irritability    of 

nerves  and  muscles. 
Consist  of  C,  H,  and  0,  the  two  latter  in  the  proportion  to 
form  water.     Include  sugars  and  starches. 


Simple  or 
monosac- 
charids 

Complex 
or  disac- 
charids 

Polysac- 
charids 


Glucose  or  dextrose  C6Hi206 
Fructose  or  levulose 


Invert 
sugar. 


Sucrose  or  cane  sugar  Ci2H22Oii. 
Lactose  or  milk  sugar  Ci2H22On. 
Maltose  or  malt  sugar  Ci2H220n. 
Starch  (C6H1005)n. 
Cellulose  (C6H1005)n. 
Glycogen  (C6H1005)n. 
Dextrin  (C6Hio05)w. 


328 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  XV 


Fats 


Proteins 


Consist  of  C,  H,  and  0,  but  the  H  content  is  relatively  high. 
Made  from  one  molecule  of  glycerine  and  three  molecules  of 
fatty  acid.     Reaction  comparable  to  neutralization  of  an 
acid  by  a  base. 

Stearic  acid  +  Glycerine  ->-         Stearin        4-  Water 
3  H.  C18H3502+C3H5(OH)3  •>•  C3H5(C18H3502)3+3  H20 
Fats  are  liquid  at  body  temperature. 
Soluble  in  ether,  chloroform,  and  hot  alcohol. 
Under  influence  of  body  enzymes  split  into  substances  out  of 
which  they  are  built.     Reaction  reverse  of  above. 
Stearin        +  Water  ->•  Glycerine  -f-  Stearic  acid 
H20  -»-  C3H5(OH)3+ 3  H.  C18H3502 

Consist  of  C,  H,  N,  0;  S,  P,  and  other  elements  may  be 

present. 
Differ  from  carbohydrates  and  fats  in  having  nitrogen,  hence 

called  nitrogenous. 

Built  up  of  simpler  substances  called  amino-acids. 
About  twenty  amino-acids  have  been  described,  and  various 

combinations  result  in  many  different  kinds  of  proteins. 
Digestion  of  proteins  means  hydrolysis  of  complex  molecules 
into    simpler    ones,     i.e.,    protein  ->-  metaprotein  ->•  pro- 
teoses  ->-  peptones  ->•  peptids  ->•  amino-acids. 
Albumins 
Globulins 
Glutelins 
Alcohol-soluble 

proteins 
Albuminoids 
Histons 
Protamins 
Nucleoproteins  —  yield 

acids  and  nuclein. 
Glycoproteins  —  yield  amino-acids 

and  a  carbohydrate. 
Phosphoproteins  -  -  yield  amino- 
acids  and  a  phospho  body. 
Haemoglobins  —  yield  amino-acids 

and  hscmatin. 

Lecithoproteins  --  yield     amino- 
acids  and  a  fatty  substance. 


Classifica- 
tion 


Simple 


Conjugated 


Yield  amino- 
acids  on 
hydrolysis. 


ammo- 


CHAP.  XV] 


SUMMARY 


329 


Proteins 


Classifica- 
tion 


Derived 


f  Primary  deriva- 
tives (formed 
through  hydro- 
lytic  changes 
which  cause 
only  slight  al- 
terations of  the 
protein  mole- 
cule) 

Secondary  derivatives 
(products  of  further 
hydrolytic  cleavage 
of  the  protein  mole- 
cule) 


Proteans. 
Metaproteins. 
Coagulated 
proteins. 


Proteoses. 
Peptones. 
Peptids. 


Accessory 
Articles 
of  Diet. 


Flavors :    The  various  oils  and  esters  that  give  odor  and 

taste  to  food. 

Condiments  :    Salt,  pepper,  mustard,  etc. 
Stimulants :     Tea,  coffee,  cocoa,  meat  extracts. 


Digestive 
Processes 


Enzymes 


Mechanical 


Chemical 


Mastication. 

Deglutition  or  swallowing. 

Peristaltic  action  of  oesophagus. 

Movements  of  stomach. 

Movements  of  intestines. 

Defecation. 

Splitting  of  complex  substances  into  simpler 
ones. 

Process  of  hydrolysis  that  is  dependent  on 
enzymes. 

Rendered  necessary  by  variety  and  com- 
plexity of  foods,  which  must  be  reduced 
to  standard  and  simple  substances  that 
the  tissues  can  use, 
Simple  sugars. 
Glycerine  and  fatty  acids. 
Amino-acids. 


Substances  produced  by  living  cells  which  act  by  catalysis. 
Efficacy  destroyed  by  boiling. 
Act  best  at  body  temperature. 
Require  medium  of  definite  reaction. 
Antecedent  or  inactive  form  called  zymogen. 
Substances  which  help  or  act  with  an  enzyme  called  co- 
enzymes. 


330 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  XV 


Enzymes 


Classification 


1.  Sugar-splitting 


a.  Inverting. 

b.  Enzymes  which  act 
on  simple  sugars. 

2.  Amylolytic  or  starch-splitting. 

3.  Lipolytic  or  fat-splitting. 

4.  Proteolytic  or  protein-splitting. 

5.  Clotting  enzymes. 

6.  Oxidizing  enzymes,  or  oxidases. 

7.  Deaminizing  enzymes. 


LIST  OF  DIGESTIVE  FLUIDS  AND   CHIEF  ENZYMES 


DIGESTIVE  FLUIDS 


Saliva 


Gastric  Fluid 


Pancreatic  Fluid 


Succus  Entericus 


Bile 


ENZYMES 


( Ptyalin    or    salivary 
\     diastase 
Pepsin 


Rennin 
Trypsin 

Diastase  or  Amylase 
Lipase  (Steapsin) 
Enterokinase 
Erepsin 

Maltase 


Inverting 


Invertase 


Lactase 


No  enzyme 


FUNCTIONS 


Hydrolyzes  starch  to  dextrin 
and  sugar  (maltose) . 

In  an  acid  medium  hydrolyzes 
proteins  into  proteoses  and 
peptones. 

Curdles  the  caseinogen  of 
milk. 

In  a  slightly  acid,  neutral,  or 
strongly  alkaline  medium, 
splits  proteoses  into  pep- 
tones and  amino-acids. 

Hydrolyzes  starch  to  dextrin 
and  sugar  (maltose). 

Splits  fats  to  glycerine  and 
fatty  acids. 

Activates  the  trypsinogen, 
and  converts  it  into  trypsin. 

Hydrolyzes  proteoses  and  pep- 
tones to  amino-acids. 

Hydrolyzes  dextrin  and  mal- 
tose to  dextrose. 

Hydrolyzes  sucrose  to  dex- 
trose and  levulose. 

Hydrolyzes  lactose  to  dex- 
trose and  galactose. 

Serves  as  coenzyme  and  acti- 
vates the  lipase  of  the  pan- 
creatic fluid. 


CHAP.  XV] 


SUMMARY 


331 


Changes 
Food 
under- 
goes in 
Mouth 


Mastication  (chewing). 
Jnsalivation  (mixing  with  saliva). 

, .      Parotid 
becreted  by  sali- 
vary glands 


and  mucous 
of  mouth. 


glands 


Result  of 


Submaxillary 
Sublingual 

f  1.  Reflex  stimulation. 
12.  Psychical. 

Consists  of  water,  mucin,  and  enzyme  —  ptyalin. 
Specific  gravity  1.004-1.008.  Alkaline  reaction. 
One  or  two  quarts  in  24  hours. 

Saliva  f  1.  Assists  in  mastication  and  de- 

glutition. 

2.  Serves  as  a  lubricant. 

3.  Dissolves  or  liquefies  the  food, 
Functions             I  thus     stimulating    the    taste 

nerves,     and     indirectly     the 
secretion  of  gastric  fluid. 

4.  Hydrolyzes    starch    to    dextrin 

and  maltose. 
Deglutition  (swallowing) . 


Stom- 
ach 
Diges- 
tion 


Movements  of  stomach. 

Serves  as  reservoir. 

Maintains  a  gradual  delivery  to  intestine. 

Time  required  for  stomach  digestion  about  5  hours. 

Psychical. 

Chemical  —  Secretin. 

Cardiac, 
becreted  by  glands 

of  stomach 


Secretion  of  gastric  fluid 


Gastric 
fluid 


True  gastric  or  peptic. 
Pyloric. 

Acid  reaction  due  to  free  hydrochloric  acid,  about 
0.2  to  0.4  per  cent. 

Pepsin. 
Enzymes       Rennin. 

Gastric  lipase. 


332 


ANATOMY  AND   PHYSIOLOGY       [CHAP.  XV 


Small 
Intestine 


Movements  of  small  ( 

[ 


rhythmic 
segmentation. 


Pancreatic 
fluid 


Secretion  of  pan-  /  Psychical. 

creatic  fluid       \  Chemical  —  secretin. 
Secreted  by  pancreas,  discharged  into  small 

intestine  during  digestion. 
Viscid  fluid,  alkaline  reaction. 

f  Trypsin. 

Enzymes  <  Diastase. 
[  Lipase. 

Secreted        by  f  1.  Intestinal      or     Lieber- 

glands  found  <      kuhn's. 

in  intestines   [  2.  Duodenal  or  Brunner's. 
Yellowish  fluid,  alkaline  reaction,   contains 

mucin. 


Bile 


Large 
Intestine 


Succus 
entericus 


Hormone  —  Secretin. 

Golden  brown  or  greenish  liquid  with  alka- 
line reaction. 

Secreted  by  liver,  stored  in  gall-bladder, 
discharged  into  small  intestine  during  di- 
gestion. 

1.  Coenzyme  —  activates  lipase  of 
pancreatic  fluid. 

2.  Digestive  secretion  —  aids  lipase 
in  hydrolysis  of  fats  and  aids  in 

Action  {      absorption  of  split  products. 

3.  Thought  to  excrete  products  of 
disintegration  of  haemoglobin. 

4.  Questioned  antiseptic  action  on 
intestinal  contents. 

/  Decompose  carbohydrates. 
\  Little  or  no  effect  on  protein. 

Movements  of  large  intestine  {  I^staltic. 

Time  required  for  food  to  pass  from  caecum  to  splenic 
flexure  about  6|  hours. 

f  Alkaline  reaction. 

Secretion    {  Contains  a  great  deal  of  mucin. 
[  No  enzymes. 

(  Hydrolysis  of  proteins  constant. 
Bacteria      <  Possible  action  on  cellulose. 
[  Benefit  doubtful. 

Undigested  and  indigestible  portions  of  food. 
Products  of  bacterial  decomposition. 
Feces          I  Great  quantities  of  bacteria. 
Bile  and  other  secretions. 
Enzymes  and  inorganic  salts. 

Defecation  —  This  term  is  applied  to  the  act  of  expelling 
the  feces  from  the  rectum. 


Bacteria 


CHAP.  XV] 


SUMMARY 


333 


Absorption 


Process  of  taking  up  digested  foodstuffs  and  carrying  them 
to  the  blood. 

Physical  —  Diffusion  and  osmosis. 
Two  Physiological  —  Reconstruction  of  end-products 

processes    |      of   digestion   into   substances   found   in   the 
blood. 

1.  Capillaries   in   the  walls   of   the   intestines. 
This   blood  is  carried  by  means   of  portal 
vein  to  liver,  from  liver  by  hepatic  veins 
to    inferior    vena    cava,    thence    to   right 
auricle. 

2.  Lymphatics  in  the  walls  of  small  intestine 
(lacteals)  absorb   digested  fats  and  empty 
into  chyle  cistern  of  thoracic  duct,  superior 
vena  cava,  and  right  auricle  of  heart. 


Paths  of 
absorption 


CHAPTER  XVI 

GENERAL  METABOLISM;  METABOLISM  OF  CARBOHYDRATES; 
METABOLISM  OF  FATS ;  METABOLISM  OF  PROTEINS.  —  DUCT- 
LESS GLANDS 

THE  nutritive  processes  in  the  human  body  include :  (1)  the 
reception  and  digestion  of  food,  followed  by  absorption  of  the  dif- 
ferent food  products,  and  the  distribution  of  these  products  to  all 
the  cells  by  the  circulating  liquids  of  the  body ;  (2)  the  absorption 
of  oxygen  by  the  circulating  liquids  in  the  lungs,  its  distribution 
to  all  the  cells  of  the  body,  and  its  union  with  the  constituents  of 
the  cells.  We  have  studied  digestion  and  absorption,  and  our 
special  problem  in  this  chapter  is  metabolism. 

METABOLISM 

General  metabolism  includes  all  the  changes  that  occur  in 
digested  foodstuffs  from  the  time  of  their  absorption  until  their 
elimination  in  the  excretions.  Sometimes  the  term  is  used  more 
specifically  to  relate  to  the  chemical  activities  that  take  place 
within  cells. 

Functions  of  metabolism.  —  Metabolic  changes  serve  two  im- 
portant purposes :  (1)  the  repair  and  growth  of  tissue,  and  (2) 
the  release  of  chemical  energy  in  the  form  of  heat,  nervous  activity, 
and  muscular  activity. 

Factors  which  promote  metabolic  changes.  —  The  factors  which 
promote  metabolic  changes  are :  (1)  enzymes,  (2)  oxygen,  and 
(3)  internal  secretions.  It  was  formerly  taught  that  the  oxygen 
absorbed  from  the  lungs  was  responsible  for  all  the  processes  of 
oxidation  that  occur  in  the  body.  More  accurate  study  has  dem- 
onstrated that  while  oxygen  is  an  important  factor,  it  is  only  one, 
and  the  enzymes  that  are  present  in  nearly  all  the  body  tissues 
are  capable  of  splitting  complex  materials  into  simpler  substances. 
Moreover,  it  is  generally  considered  that  the  action  of  the  tissue 

334 


CHAP.  XVI]  GENERAL   METABOLISM  335 

enzymes  comes  first  and  causes  splitting  by  hydrolysis,  then  other 
enzymes  termed  oxidases  activate  the  process  of  oxidation. 

Metabolic  changes.  —  These  chemical  changes  can  be  classified 
under  two  heads :  (1)  anabolism,  or  the  building-up  processes, 
and  (2)  katabolism,  or  the  splitting  of  complex  substances  into 
simpler  ones.  The  most  important  are  as  follows :  — 

A.  The  cells  take  from  the  blood  the  substances  which  they 
require  for  repair  and  growth,  and  build  it  up  into  protoplasm. 
This  involves  the  conversion  of  non-living  material  into  the  living 
protoplasm  of  the  cells,  and  is  an  example  of  anabolism. 

B.  Oxidation,  or  the  union  of  oxygen  with  the  constituents  of 
the  cells,  resulting  in  the  release  of  energy  and  the  breaking  down 
of  complex  substances  into  simpler  products.     This  is  an  example 
of  katabolism. 

Some  of  the  simpler  products  that  result  from  oxidation  are 
acids.  These  acids  must  be  eliminated  or  changed  chemically, 
as  all  the  digestive  fluids  of  the  body,  with  the  exception  of  the 
gastric  fluid,  are  alkaline  or  neutral,  and  this  condition  is  essential 
to  nutrition  and  even  to  the  immediate  continuance  of  life,  (a) 
Some  of  the  weaker  acids  are  eliminated  in  the  urine ;  one,  carbonic 
acid  (H2CO3),  is  a  very  unstable  compound  and  breaks  down  to 
form  water  (H2O)  and  carbon  dioxide  (€02).  (6)  When  proteins 
are  oxidized,  sulphur  is  set  free.  This  sulphur  (S)  unites  with 
water  (H2O)  and  oxygen  (O2)  to  form  sulphuric  acid  (H2SO4). 
Sulphuric  acid  is  promptly  neutralized  by  the  alkalies  present  in 
the  tissues,  so  that  the  body  never  contains  sulphuric  acid  but 
does  contain  sulphates  and  water,  which  result  from  the  process 
of  neutralization.  (See  page  8.) 

C.  The  conversion  of  glucose  into  glycogen,  and  the  reconversion 
of  glycogen  into  glucose. 

D.  The  conversion  of  glucose  into  fat. 

E.  The  conversion  of  fat  into  glucose. 

F.  The  conversion  of  amino-acids  to  glucose. 

G.  The  conversion  of  amino-acids  to  fat. 

METABOLISM   OF  CARBOHYDRATES 

It  is  convenient  to  consider  the  history  of  carbohydrates  under 
three  heads :  (1)  its  supply ;  (2)  its  storage ;  and  (3)  its  consump- 
tion. 


336  ANATOMY  AND  PHYSIOLOGY      [CHAP.  XVI 

(1)  The  supply  is  regulated  by  the  diet. 

(2)  The  storage  is  provided  for  temporarily  by  the  liver,  the 
muscles,  and  the  cells  of  all  tissues. 

During  the  process  of  digestion  all  the  carbohydrates  are  changed 
to  simple  sugars.  It  is  possible  that  a  small  amount  of  sugar  is 
absorbed  in  the  stomach,  but  by  far  the  greater  part  passes  into 
the  capillaries  of  the  small  intestine.  These  capillaries  pour  their 
contents  into  the  portal  vein,  which  carries  the  blood  rich  with 
glucose  to  the  liver.  The  liver  cells  take  this  glucose  from  the 
blood,  and  by  putting  together  a  number  of  molecules  and  with- 
drawing water,1  the  soluble  glucose  is  changed  to  insoluble  glyco- 
gen,  which  is  stored  in  the  liver  cells.  In  thus  storing  up  glycogen 
and  doling  it  out  as  needed,  the  liver  helps  to  maintain  the  normal 
quantity  of  glucose  —  0.1  to  0.15  per  cent  —  in  the  blood.  From 
the  blood  stream  glucose  is  taken  up  by  the  muscles  and  other 
cells  and  stored  as  glycogen  until  needed,  or  it  may  be  oxidized  at 
once.  The  maximum  storage  of  glycogen  in  the  body  is  about 
one  pound.  This  means  that  the  formation  of  glycogen  cannot 
continue  indefinitely,  and  if  the  carbohydrate  intake  is  in  excess 
of  the  current  consumption,  conditions  are  favorable  for  the  de- 
velopment of  fat  from  the  surplus  carbohydrates.  This  trans- 
formation is  a  well-established  and  frequent  occurrence  and  is 
probably  responsible  for  much  of  the  obesity  which  is  such  a  com- 
mon condition. 

(3)  At  the  consumption  end  the  amount  of  sugar  oxidized  is 
controlled  by  the  energy  needs  of  the  tissues,  particularly  the 
muscles. 

Factors  controlling  the  metabolism  of  carbohydrates.  —  The 
metabolism  of  carbohydrates  is  under  the  control  of  the  nervous 
system,  but  how  this  control  is  maintained  is  still  an  open  question. 
One  view  is  that  there  is  a  sugar  regulating  centre  which  may 
be  influenced  by  the  amount  of  sugar  in  the  blood,  just  as  the 
respiratory  centre  is  influenced  by  the  amount  of  carbon  dioxide  in 
the  blood.  If  this  is  true,  the  way  in  which  this  centre  exerts  its 
control  is  complicated  and  indirect.  There  is  much  evidence  to 
support  the  view  that  the  internal  secretion  of  the  adrenal  glands, 
of  the  pancreas,  and  of  the  hypophysis  play  a  very  important  part. 

1  This  is  a  process  of  dehydration  and  is  exactly  the  opposite  of  hydrolysis.     See 

p.'ure  8. 


CHAP.  XVI]  GENERAL  METABOLISM  337 

Functions  of  carbohydrates.  —  The  oxidation  of  glucose  serves 
the  following  purposes :  (1)  It  furnishes  the  main  if  not  the  only 
source  of  energy  for  muscular  work,  and  for  all  the  nutritive 
processes  of  the  body.  (2)  It  furnishes  an  important  part  of 
the  heat  needed  to  maintain  the  body  temperature.  (3)  It  pre- 
vents oxidation  of  the  body  tissues,  because  it  constitutes  a  re- 
serve fund  that  is  the  first  to  be  drawn  upon  in  time  of  need. 
(4)  An  excess  of  carbohydrates  over  and  above  what  can  be 
stored  as  glycogen  in  the  liver  and  muscles  is  converted  into  adi- 
pose tissue. 

Waste  products  of  carbohydrate  metabolism.  —  The  waste 
products  resulting  from  the  oxidation  of  glucose  are  carbon  dioxide 
(CO2)  and  water  (H2O).  This  process  is  thought  to  be  compar- 
able to  the  fermentation  of  sugar  outside  the  body,  and  the  same 
substances  are  formed,  viz.  alcohol,  acids,  carbon  dioxide,  and 
water. 

Derangements  of  carbohydrate  metabolism.  —  The  storage  of 
glycogen  may  be  deranged  by  injuries  to  the  central  nervous  sys- 
tem or  by  hypersecretion  of  the  adrenal  glands  or  the  hypophysis, 
in  which  case  hyperglycemia  (excessive  amount  of  sugar  in  blood) 
and  glycosuria  (sugar  in  the  urine)  result.  Or  the  liver  and 
muscles  may  be  unable  to  store  all  the  sugar  absorbed  from  the 
alimentary  canal,  and  in  this  case  there  is  temporary  hypergly- 
cemia and  glycosuria.  Inability  to  oxidize  the  sugar  at  the 
consumption  end  brings  on  a  hyperglycemia  and  glycosuria  of  a 
serious  nature. 

Diabetes  mellitus.  —  Defective  sugar  metabolism  is  the  central 
condition  in  this  disease.  When  the  body  cannot  oxidize  sugar, 
the  continual  addition  of  digested  sugar  to  the  blood  leads  to 
hyperglycemia.  When  this  state  is  reached,  i.e.,  the  concentration 
of  sugar  in  the  blood  exceeds  the  normal  limit,  the  kidneys  abstract 
it,  and  allow  it  to  escape  in  the  urine.  .  In  severe  cases  all  the  sugar 
entering  the  blood  passes  into  the  urine  without  having  con- 
tributed to  the  activities  of  the  tissues.  The  inability  to  oxidize 
sugar  is  accompanied  by  inability  to  make  and  hold  glycogen  in  the 
liver  and  muscles.  When  diabetes  reaches  its  full  intensity,  and 
no  sugar  can  be  broken  down,  there  follows  a  faulty  fat  metabolism 
and  acidosis  of  the  gravest  kind.  (See  page  338.) 


338  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XVI 

METABOLISM   OF  FATS 

The  tendency  of  recent  work  is  to  favor  the  view  that  after 
fat  is  split  into  glycerine  and  fatty  acids,  it  is  absorbed  by  the 
epithelial  cells  of  the  villi  and  reconstructed  in  the  very  act  of 
passing  through  them.  This  reconstruction  is  not  a  mere  repro- 
duction of  the  original  fat.  The  glycerine  and  fatty  acids  combine 
in  such  proportion  as  to  make  the  fat  characteristic  of  the  human 
animal.  This  fat  passes  into  the  lacteals  of  the  villi.  From  these 
small  lacteals  it  must  find  its  way  through  the  larger  lymphatics 
in  the  mesentery  to  the  thoracic  duct,  and  then  through  the 
thoracic  duct  to  the  blood.  This  fat  is  carried  by  the  blood  to 
all  the  different  parts  of  the  body,  and  the  tissues  slowly  take  it 
out  as  they  need  it  in  their  metabolic  processes.  Within  the 
tissues  it  serves  as  fuel  and  is  oxidized  to  supply  the  energy  needs 
of  the  cells.  If  fat  is  burned  outside  the  body,  heat  is  liberated, 
and  the  waste  products  are  carbon  dioxide  and  water.  This  pro- 
cess is  similar  to  the  one  that  takes  place  in  the  body.  Fat  that  is 
not  required  for  the  production  of  energy  is  stored  up  in  certain 
parts  of  the  body,  but  not  all  the  adipose  tissue  found  in  the  body 
is  derived  from  fats,  as  excess  carbohydrates  are  also  stored  as 
fat.  In  addition  there  is  a  possibility  that  fat  may  be  formed 
from  proteins.  The  amino-acids  resulting  from  protein  digestion, 
if  in  excess  of  what  are  needed  to  reconstruct  body  proteins,  may 
be  converted  to  sugar  and  glycogen,  also  to  fat. 

Functions  of  fat.  —  The  uses  of  fat  are  (1)  to  serve  as  fuel  and 
yield  heat  and  other  forms  of  energy.  (2)  To  provide  a  store  of 
reserve  food  to  be  drawn  upon  in  time  of  need.  When  the  supply 
of  food  is  insufficient,  or  in  diseased  conditions,  the  body  oxidizes 
first  the  glycogen  stored  in  the  muscles  and  liver,  and  then  the  fat 
stored  in  adipose  tissue.  (3)  It  acts  as  a  protein  sparer.  In  ex- 
treme conditions,  when  there  is  no  glycogen  or  fat  available,  the 
body  may  oxidize  the  proteins  of  the  tissues.  If  the  supply  of 
fat  is  large,  it  follows  that  the  proteins  of  the  tissues  will  be  pro- 
tected. 

Derangements  of  fat  metabolism.  —  When  fat  is  fully  oxidized 
the  only  end-products  are  carbon  dioxide  and  water.  In  certain 
diseased  conditions,  for  instance,  severe  diabetes,  the  oxidation  of 
fat  is  incomplete,  and  certain  compounds  of  an  acid  character  are 


CHAP.  XVI]  GENERAL   METABOLISM  339 

formed.     These  may  accumulate  and  be  responsible  for  a  condi- 
tion of  severe  poisoning  called  acidosis. 

The  cause  of  obesity.  —  This  condition  is  usually  caused  by 
eating  more  food  than  the  body  needs,  especially  fat  and  carbo- 
hydrates. The  excess  is  stored  as  glycogen  and  adipose  tissue. 
The  needs  of  different  individuals  vary,  depending  on  their  mode 
of  life,  and  on  their  capacity  to  oxidize  food  materials,  so 'that  a 
diet  which  will  give  an  excess  to  one  individual  may  in  the  body  of 
another  be  entirely  consumed.  A  sedentary  life  and  absence  of 
worry  lessen  the  oxidation  of  food  products  and  increase  the  ten- 
dency to  take  on  flesh,  while  a  very  active  muscular  life  has  the 
opposite  effect. 

METABOLISM   OF  PROTEINS 

As  a  result  of  digestion,  proteins  are  hydrolyzed  to  amino-acids, 
and  are  absorbed  by  the  blood  capillaries  of  the  villi.  From  the 
intestines  this  blood  passes  through  the  liver  before  it  reaches  the 
general  circulation.  Because  of  this  it  is  considered  possible  that 
one  stage  in  the  metabolism  of  some  of  these  amino-acids  may  be 
carried  out  in  the  liver.  After  a  meal  the  amino-acids  in  the  blood 
are  increased  in  amount  and  are  carried  to  all  the  tissues.  The 
fate  of  these  bodies  varies.  They  may  be  taken  up  by  the  tissues, 
combined  to  form  proteins,  and  used  (1)  during  the  period  of  growth 
to  build  up  new  tissue,  and  (2)  both  in  youth,  and  after  growth  has 
ceased,  to  replace  tissue  that  has  been  oxidized.  Or  they  may  split 
at  once  into  a  nitrogenous  and  non-nitrogenous  part.  The  nitrog- 
enous part  passes  to  the  liver,  and  is  transformed  into  urea  to  be 
excreted  by  the  kidneys.  The  non  nitrogenous  part  is  used  in 
the  formation  of  sugar  and  fat,  and  may  be  stored  as  glycogen 
and  adipose  tissue.  Sooner  or  later  it  is  oxidized,  liberating  energy. 

Functions  of  proteins.  —  We  have  seen  that  the  main  function  of 
proteins  is  to  build  up  tissue,  and  they  are  the  one  class  of  foods 
capable  of  doing  this.  In  addition  they  serve  the  same  purpose  as 
carbohydrates  and  fats  and  may  even  be  converted  into  adipose 
tissue. 

Nutritive  value  of  different  proteins.  —  Proteins  vary  in  their 
constituents  and  in  their  nutritive  value.  Because  of  this  they  are 
classed  as  adequate  and  inadequate  proteins.  Adequate  proteins 
contain  all  the  constituents  for  the  growth  and  maintenance  of 


340  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVI 

the  body.  Inadequate  proteins  furnish  material  for  energy  needs, 
but  not  for  growth  and  the  repair  of  tissue  waste.  The  difference 
between  the  two  kinds  seems  to  lie  in  the  character  of  the  ammo- 
acids  of  which  they  are  composed.  Gelatine  is  an  example  of  an 
inadequate  protein.  It  is  easily  digested  and  absorbed,  under- 
goes oxidation,  which  results  in  the  liberation  of  energy  and  the 
production  of  urea,  carbon  dioxide,  and  water,  but  it  does  not 
supply  the  material  needed  for  the  repair  of  tissue  waste.  On  the 
other  hand,  the  casein  of  milk  and  the  glutenin  of  wheat  contain 
all  the  essential  amino-acids  and  not  only  furnish  energy,  but  can 
build  tissue. 

Nitrogen  equilibrium.  —  The  protein  molecules  are  characterized 
by  containing  16  per  cent  of  nitrogen.  After  the  metabolism  of 
protein,  nitrogen  is  eliminated  chiefly  in  the  urine,  and  to  a  limited 
extent  in  the  feces.  The  body  is  said  to  be  in  nitrogen  equilibrium 
when  the  amount  of  protein  nitrogen  taken  into  the  body  is  equal 
to  the  amount  eliminated  in  the  excreta.  If  there  is  a  plus  balance 
in  favor  of  the  food,  it  means  that  protein  is  being  stored  in  the 
body,  and  this  is  an  ideal  condition  during  the  period  of  growth 
or  convalescence  from  wasting  illness.  If  the  balance  is  minus, 
the  body  must  be  losing  protein,  but  under  normal  conditions  this 
does  not  occur.  Nitrogen  equilibrium  may  be  maintained  at 
various  levels.  That  is,  the  amount  of  food  eaten  may  be  in- 
creased or  decreased  to  a  considerable  degree  without  disturbing 
the  equilibrium.  This  means  that  the  greater  the  amount  of  ni- 
trogen ingested,  the  greater  the  amount  excreted.  If  nitrogen 
equilibrium  can  be  estimated  at  various  levels,  the  practical  ques- 
tion which  arises  is :  At  what  level  should  it  be  maintained  to 
secure  the  best  results?  This  question  is  difficult  to  answer. 
The  average  diets  recommended  range  from  75-130  gms.  protein 
per  day,  but  experiments  have  shown  that  for  considerable  periods 
the  body  can  be  maintained  on  35-40  gms.  Our  present  knowledge 
does  not  warrant  our  stating  that  one  is  better  or  worse  off  for  an 
excessively  low  protein  diet. 

Flavors  and  condiments.  —  The  most  important  service  rendered 
by  these  bodies  is  that  by  making  the  food  appetizing  they  increase 
the  secretion  of  gastric  fluid. 

Stimulants.  —  Under  this  heading  is  included  tea,  coffee,  cocoa, 
and  meat  extracts.  Tea  and  coffee  owe  their  stimulating  action 


CHAP.  XVI]  GENERAL   METABOLISM  341 

to  caffeine.  Cocoa,  or  the  chocolate  made  from  it,  contains 
nourishment  in  the  form  of  carbohydrate,  fat,  and  protein.  Its 
stimulating  effects  are  due  to  theobromin,  and  are  similar  to  those 
of  caffeine.  Meat  extracts  contain  secretogogues  which  stimulate 
the  gastric  glands  to  secretion,  but  aside  from  this  have  little 
nutritive  value. 

Alcohol.  —  Alcohol  is  rapidly  absorbed  and  quickly  oxidized. 
It  yields  heat,  and  gives  rise  to  carbon  dioxide  and  water.  It  is 
not  transformed  into  fat  or  glycogen,  hence  is  not  stored.  In- 
directly it  may  cause  obesity  in  two  ways  :  (1)  moderate  drinking 
creates  a  keen  appetite  and  so  favors  overeating ;  (2)  the  oxidation 
of  alcohol  lessens  the  need  for  the  oxidation  of  fats  or  carbohy- 
drates. Thus  fat  is  spared  to  be  accumulated,  or  carbohydrates 
to  be  changed  into  it. 

Energy  value  of  food.  —  All  the  energy  required  for  muscular 
work  may  be  derived  from  the  carbohydrates  and  fats  provided 
they  are  supplied  in  sufficient  quantities.  If  they  are  not,  then 
protein  is  used  as  a  source  of  energy.  If  there  is  an  abundance  of 
non-nitrogenous  food,  the  amount  of  nitrogen  excreted  remains 
pretty  constant.  Exercise  does  not  increase  it,  neither  does  sleep 
decrease  it. 

In  health  the  temperature  of  the  body  is  comparatively  constant,1 
despite  the  changes  in  outside  temperature.  The  supply  of  heat 
needed  to  maintain  this  constant  temperature  is  derived  from  the 
oxidation  of  non-protein  food.  The  amount  of  chemical  energy 
in  any  substance  determines  its  heat  value.  This  may  be  as- 
certained by  burning  the  substances  and  noting  the  amount  of 
heat  given  off.  It  matters  little  whether  the  burning  occurs  in  a 
test  tube  or  in  the  living  body.  The  heat  produced  is  measured 
in  terms  of  calories  by  means  of  a  calorimeter.  A  large  calorie 
(cal.)  is  the  amount  of  heat  required  to  raise  one  kilogram  of 
water  1°  C.  The  large  calorie  (Cal.)  is  the  one  referred  to  in  physi- 
ology. As  the  result  of  many  tests  the  caloric  value  of  the  different 
foodstuffs  has  been  found  to  be  as  follows : 2 

Carbohydrate  1  gm.  =  4  cal. 
Fat  1  gm.  =  9  cal: 

Protein  1  gm.  =  4  cal. 

1  See  page  389. 

2  These  figures  are  lower  than  those  usually  given,   e.g.,   carbohydrate  4.1,  fat 
9.3,  and  protein  4.1,  which  are  now  known  to  allow  too  little  for  losses  in  digestion. 


342  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVI 

The  amount  of  food  necessary  for  normal  nutrition.  —  In  a 
normal  condition  the  main  object  of  food  is :  (1)  to  furnish  the 
material  for  the  growth  and  maintenance  of  tissue,  and  (2)  to  fur- 
nish energy  for  heat,  muscular  work,  etc.  The  most  important 
factors  influencing  the  amount  of  food  required  are  age,  activity, 
and  in  lesser  degree,  size,  shape,  body  composition,  lactation,  and 
climate.  The  greater  the  amount  of  muscular  work,  the  greater 
the  amount  of  food  required.  Children  need  more  food  in  propor- 
tion to  their  weight  than  adults,  because  they  are  more  active  in- 
ternally and  externally,  and  in  addition  must  provide  for  the 
growth  of  new  tissue.  Increased  age  usually  means  less  active  life 
as  well  as  less  active  metabolism  and  thus  less  food  is  required. 
Women,  as  a  rule,  require  less  food  than  men,  because  they  are 
smaller,  have  less  active  tissue  in  proportion  to  weight,  and  tend 
to  more  sedentary  life.  In  an  extremely  cold  climate  more  food  is 
required  for  heat  production  in  order  to  make  up  for  the  loss  of 
heat  from  the  body.  It  is  ordinarily  estimated  that  the  daily  diet 
should  yield  between  2300  and  2400  calories  for  an  individual 
weighing  60  kilograms  (130  Ib.) ;  that  is,  about  40  calories  for  each 
kilogram  of  body  weight. 

An  excellent  authority  on  this  subject  recommends  that  the 
daily  diet  be  arranged  about  as  follows :  — 

CALORIES 

Carbohydrate  275  gm.  X  4  =  1100 

Fat                   100  gm.  X  9  =  900 

Protein               75  gm.  X  4  =  300 

Total  2300 

Within  certain  limits  the  fats  and  carbohydrates  may  be  sub- 
stituted for  each  other.  For  a  healthy  person  leading  a  normal 
life  appetite  and  experience  seem  safe  guides  by  which  to  control 
the  diet.  They  will  at  least  prevent  undernutrition,  and  the  con- 
sequent lessening  of  the  body's  natural  powers  of  resistance  to 
disease.  The  opposite  danger  of  overeating  is  a  real  one,  because  an 
excess  of  food  puts  unnecessary  strain  upon  the  organs  of  nutrition 
and  excretion,  and  favors  the  formation  of  excessive  adipose  tissue. 
Excess  of  proteins  may  overload  the  system  with  the  products  of 
intestinal  putrefaction.  Excess  of  carbohydrates  may  cause  flatu- 
lence, due  to  fermentation  of  these  foods.  An  excess  of  fat  in- 
terferes with  digestion  by  retarding  the  secretion  of  gastric  fluid. 


CHAP.  XVI]  DUCTLESS  GLANDS  343 

Vitamines.  —  Many  nutrition  experiments  have  made  it  evi- 
dent that  for  growth  and  maintenance  the  human  animal  requires 
not  only  certain  amounts  of  proteins,  carbohydrates,  and  fats,  but 

-    certain  other  essential  substances  called  vitamines.     (It  has  been 

i  suggested  that  food  hormones  would  be  a  better  name.)  They 
do  not  serve  as  a  source  of  energy  and  probably  not  as  direct 
building  stones,  but  they  are  in  some  (as  yet  undetermined)  way 
essential  to  metabolism.  Various  animals  have  been  fed  on  special 

I  diets  amply  covering  all  the  needs  in  the  way  of  protein,  carbohy- 
drate, and  fat,  but  not  foods  containing  vitamines.  Young  animals 
grow  for  a  certain  time,  then  come  to  a  standstill,  sicken,  and  die 
unless  food  containing  vitamines  is  added  to  the  diet.  Other 

j  experiments  have  led  some  observers  to  suggest  that  certain  dis- 
eases such  as  beriberi,  scurvy,  and  pellagra  are  caused  by  a  de- 
ficiency of  vitamines  in  the  diet.  Vitamines  are  present  in  cer- 
tain foods  and  absent  in  others.  They  are  found  in  fresh  fruit 
juices,  milk,  eggs,  and  in  the  bran  of  wheat,  rice,  and  other  cereals. 

DUCTLESS  GLANDS 

The  ductless  glands  form  a  group  of  organs  that  produce  secre- 
tions, called  internal  secretions,  which  leave  the  gland  by  the  blood 
or  lymph,  and  not  by  means  of  a  duct.  Many  of  the  glands  that 
possess  ducts  and  form  an  external  secretion  form  an  internal 
secretion  as  well,  i.e.,  the  liver  and  pancreas,  but  these  are  not 
classed  as  ductless,  because  the  external  secretion  is  carried  out 
of  the  gland  by  means  of  a  duct,  though  the  internal  secretion  passes 
into  the  blood  or  lymph  just  as  in  the  ductless  glands.  The  func- 
tion of  the  ductless  glands  is  intimately  connected  with  the  pur- 
pose of  the  internal  secretions,  and  this  is  imperfectly  understood.1 
However,  a  diseased  condition  or  removal  of  these  glands  pro- 
duces symptoms  which  make  evident  their  importance  in  the  nor- 
mal carrying  out  of  the  body  functions. 

The  most  important  ductless  glands  are :  — 

.   (1)  The  Thyroid.  (5)  The  Hypophysis. 

(2)  The  Parathyroids.  (6)  The  Epiphysis  (Pineal  body). 

(3)  The  Thymus.  (7}  The  Testes  (see  page  477). 

(4)  The  Adrenals  (supra-renal  capsules) .  (8)  The  Ovaries  (see  page  463). 

1  See  page  149. 


344 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVI 


(1)  The  thyroid. — The  thyroid  is  a  small,  flat  gland  lying 
against  the  fore  part  of  the  trachea,  below  the  thyroid  cartilage. 
It  is  of  a  deep  red  color,  weighs  about  an  ounce  (30  gms.),  and 
consists  of  two  lateral  lobes  connected  at  their  lower  parts  by  an 
isthmus.  The  lobes  are  broader  below  and  taper  to  a  point  above. 
Small  masses  of  thyroid  tissue  are  sometimes  found  along  the 


BIGHT   LOBE    OF, 
THYROID    BODY 


.    PYRAMID    OF 
THYROID    BODY 


FIG.  179.  —  THE  THYROID  Bopy  AND  THE  RELATED  BLOOD-VESSELS.     (Gerrish.) 

trachea  as  far  down  as  the  heart.  They  are  called  accessory 
thyroids.  Comparatively  little  is  known  about  the  action  of  the 
thyroid  secretion,  but  much  clinical  evidence  supports  the  theory 
that  it  is  necessary  for  the  continuance  of  normal  metabolism. 

Cretinism  is  a  condition  caused  by  congenital  defects  of  the 
thyroid  or  atrophy  occurring  in  early  life.  The  growth  of  the 
skeleton  ceases  and  there  is  complete  arrest  of  mental  develop- 
ment. Children  so  afflicted  are  not  only  dwarfed,  but  ill-propor- 
tioned, having  heavy  heads  and  abdomens  and  weak  muscles. 

Myxcedema  is  a  disturbed  condition  of  metabolism  that  fol- 
lows the  removal  or  atrophy  of  the  gland.  The  individual  so 


CHAP.  XVI]  DUCTLESS   GLANDS  345 

afflicted  presents  a  peculiar  appearance,  as  the  subcutaneous  con- 
nective tissue  becomes  thickened,  the  face  and  hands  swollen  and 
puffy.  The  mental  faculties  become  blunted  and  idiocy  results 
unless  proper  treatment  is  instituted. 

Cretinism  and  myxoedema  are  both  supposed  to  be  due  to  a 
lack  of  the  internal  secretion  of  the  thyroid,  and  much  success  has 
followed  the  administration  of  thyroid  extract  in  various  ways. 

Goitre  is  a  condition  in  which  the  gland  is  enlarged,  but  the  se- 
cretion may  not  be  interfered  with. 

Exophthalmic  goitre  is  a  disease  characterized  by  extreme  ner- 
vousness, quickened  heart  action,  protruding  eyeballs,  and  goitre. 
It  is  caused  by  an  overabundant  production  of  thyroid  secretion, 
due  to  enlargement  and  overactivity  of  the  gland. 

(2)  The    parathyroids.  —  Embedded   in  the    surface   of    each 
lateral  lobe  of  the  thyroid  are  two  little  masses,  each  about  one- 
fourth  inch  (6.25  mm.)  in  diameter.     They  are  solid  accumula- 
tions of  epithelioid  cells,  invested  with  a  tunic  of  areolar  tissue 
and  well  supplied  with  blood-vessels.     The  function  of  the  para- 
thyroids is  supposed  to  consist  in  neutralizing  toxic  substances 
formed  elsewhere  in  the  body.     In  their  absence  acute  tetanic 
convulsions  develop. 

(3)  The  thymus.  —  The  thymus  is  a  temporary  organ  attain- 
ing its  full  size  at  the  end  of  the  second  year.     Then  it  ceases  to 
grow  and  remains  practically  stationary  until  puberty,  at  which 
time  it  degenerates.     At  the  period  of  most  active  growth  it  con- 
sists of  two  lateral  lobes  situated  below  the  thyroid  and  in  front 
of  the  trachea. 

The  function  of  this  gland  is  not  known,  but  it  is  thought  to 
have  a  definite  connection  with  growth  and  with  the  development 
of  the  reproductive  organs. 

(4)  The  adrenals  or  supra-renal  capsules.  —  The  adrenals  are 
small  flattened  bodies  of  a  yellowish  color  which  are  placed  one 
above  each  kidney.     They  secrete  a  substance  called  adrenalin, 
which  owes  its  power  to  adrenin  or  epinephrin.     This  secretion 
raises  the  blood-pressure,  slows  the  heart,  and  increases  the  amount 
of  sugar  in  the  blood.     The  rise  in  blood-pressure  is  due  to  the 
contraction  of  the  blood-vessels,  especially  those  of  the  abdominal 
viscera.     These  glands  are  supplied  with  secretory  nerves  which 
may  be  stimulated  reflexly.     Sensory  stimuli  and  strong  emotions 


346  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVI 

increase  the  activity  of  the  gland.  On  the  strength  of  these  facts 
it  has  been  suggested  that  the  adrenals  are  emergency  organs;  that 
at  times  of  great  emotional  stress,  fear,  anger,  etc.,  their  secretion 
is  increased,  resulting  in  an  increased  blood-supply  for  the 
muscles,  as  well  as  a  rapid  transformation  of  glycogen  into 


FIG.  180.  —  THE  THYMUS,  THE  STERNAL  AND  COSTAL  CARTILAGES  HAVING  BEEN 
REMOVED.     (Gerrish.) 

sugar,  which  at  once  enters  the  blood,  and  is  readily  available 
for  the  production  of  energy. 

Another  service  of  adrenin  is  to  postpone  fatigue.  A  very 
small  addition  of  adrenin  to  the  blood  of  an  animal  whose  strength 
is  flagging  may  give  a  renewed  command  of  the  muscles.  It  is 
now  believed  that  "  the  strength  of  desperation  "  is  due  to  the 
timely  discharge  of  adrenin  into  the  blood. 

Under  conditions  of  rest  the  adrenals  exercise  considerable 
influence,  for  if  they  are  removed  or  wasted  by  disease,  several 
indispensable  hormones  seem  to  be  lost.  In  such  cases  the 
victim  grows  weak,  suffers  from  incessant  nausea,  and  dies  as 
though  from  exhaustion. 

(5)  The  hypophysis.  —  The  hypophysis,  also  called  the  pitui- 
tary body,  is  of  an  ovoid  form,  a  reddish  gray  color,  and  consists 
of  two  lobes.  The  anterior  lobe  is  larger  and  distinctly  glandular, 


CHAP.  XVI]  DUCTLESS  GLANDS  347 

the  posterior  lobe  is  smaller  and  composed  of  nerve-cells  and 
fibres. 

The  pituitary  is  lodged  in  a  depression  of  the  middle  portion 
of  the  sphenoid  bone,  and  is  firmly  held  in  place  by  the  dura 
mater.1 

From  the  results  of  various  experiments  it  is  evident  that  the 
pituitary  body  is  essential  to  normal  metabolism,  and  moreover 
that  the  anterior  and  posterior  lobes  exercise  different  functions. 
This  differentiation  in  function  cannot  be  made  complete,  but  it 
would  seem  that  the  anterior  lobe  furnishes  a  secretion  which 
stimulates  the  growth  of  the  skeleton,  possibly  of  all  the  connective 
tissues,  and  in  addition  exerts  some  essential  influence  on  metab- 
olism. The  posterior  lobe  furnishes  several  hormones  which 
have  a  stimulating  effect  on  the  tone  of  plain  muscle,  the  secretory 
activity  of  several  glands,  and  the  process  of  glycogenolysis  (chang- 
ing glycogen  to  glucose).  In  addition  it  shares  with  the  thymus 
and  adrenals  a  regulating  influence  upon  the  normal  development 
of  the  reproductive  organs. 

Gigantism,  or  excessive  growth,  and  dwarfism,  or  underdevelop- 
ment,  are  thought  to  be  due  to  abnormal  conditions  of  this  gland 
in  early  life.  In  later  life  abnormal  conditions  are  attended  with 
enlargement  of  the  bones  of  the  extremities  and  the  features  of 
the  face,  a  condition  known  as  acromegaly. 

(6)  The  epiphysis.  —  The  epiphysis  or  pineal  body  is  a  small 
reddish  gray  body  located  in  the  third  ventricle  of  the  brain.  In 
early  life  it  is  glandular  and  attains  its  maximum  growth  about 
the  seventh  year.  After  this  period,  and  particularly  after  puberty, 
it  decreases  in  size,  and  the  glandular  tissue  is  replaced  by  fibrous 
tissue.  It  is  thought  that  in  early  life  the  gland  furnishes  a 
secretion  that  inhibits  growth,  and  restrains  the  development  of 
the  reproductive  glands. 

SPLEEN 

Some  authorities  class  the  spleen  with  the  ductless  glands ; 
other  authorities  question  this,  as  it  has  not  been  possible  to 
demonstrate  that  it  furnishes  an  internal  secretion.  It  is  directly 
beneath  the  diaphragm,  behind  and  to  the  left  of  the  stomach,  and 
is  covered  by  the  peritoneum.  It  is  bean-shaped,  convex  on  the 

1  See  page  410. 


348 


ANATOMY  AND  PHYSIOLOGY     [CHAP.  XVI 


outer  surface,  concave  on  the  inner,  and  weighs  usually  from  five 
to  eight  ounces  (150  to  240  gms.).  Beneath  the  serous  coat  it  is 
covered  by  a  fibrous  and  muscular  capsule  which  sends  fibrous 

bands  (trabecules)  to 
form  a  network  in  the 
interior  of  the  organ. 
The  meshes  of  this 
fibrous  framework  are 
filled  with  a  substance 
called  spleen  pulp. 

Blood  supply.  —  Blood 
is  supplied  to  the  spleen 
by  the  splenic  artery, 
which  enters  the  concave 
side  of  the  spleen  at  a 
depression  called  the 
hilus.  The  arrangement 
of  the  blood-vessels  is 
peculiar  to  this  organ. 
The  splenic  artery  divides 
into  several  branches  be- 
fore entering  the  organ, 
and  after  entering 
rapidly  divides  into 
smaller  vessels.  When  the  minute  arteriole  stage  is  reached,  the 
vessels  terminate,  and  the  blood  escapes  into  the  spleen  pulp.  The 
blood  is  collected  from  the  pulp  by  thin-walled  veins,  which  unite 
to  form  the  splenic  vein.  The  splenic  vein  unites  with  the  superior 
mesenteric  to  form  the  portal  vein,  and  carries  the  blood  to  the 
liver. 

Functions.  —  The  functions  of  the  spleen  are  imperfectly  under- 
stood, but  it  is  usually  credited  with  the  following :  — 

(1)  The  formation  of  red  cells  during  foetal  life  and  for  a  short 
period  after  birth. 

(2)  The  presence  of  a  large  amount  of  iron  suggests  that  it  may 
help  in  the  preparation  of  new  haemoglobin,  or  in  the  preservation 
of  the  iron  set  free  by  the  death  of  the  red  cells.     The  presence  of 
iron  was  formerly  considered  an  evidence  that  the  red  cells  were  de- 
stroyed in  the  spleen,  but  this  is  not  accepted  at  the  present  time. 


FIG.  181.  —  THE  SPLEEN,  SHOWING  THE 
GASTRIC  AND  RENAL  SURFACES  AND  THE 
BLOOD-VESSELS.  (Gerrish.) 


CHAP.  XVI] 


SUMMARY 


349 


(3)  The  spleen  increases  in  size  during  digestion ;   after  diges- 
tion is  over  it  returns  to  its  usual  size.     It  is  always  large  in 
well-fed,  and  small  in  starved  animals.     This  supports  the  belief 
that  it  may  be  concerned  in  digestion  or  metabolism. 

(4)  It  is  probable  that  the  spleen  is  concerned  in  the  production 
of  uric  acid.     Various  waste  products  that  result  from  the  metab- 
olism of  proteins  are  found  in  the  spleen,  and  it  is  thought  that  by 
the  action  of  special  enzymes  these  substances  are  changed  to  uric 
acid. 

(5)  In  certain  diseases,  more  especially  typhoid  and  malaria, 
a  temporary  enlargement  takes  place.     Some  physiologists  inter- 
pret this  as  an  evidence  that  the  spleen  has  an  important  protec- 
tive function. 


Metabolism 


Functions 


Dependent 
upon 

Equals  the 
sum  of  the 


SUMMARY 

Refers  to  changes  that  occur  in  foodstuffs  from  time  of 
absorption  to  elimination.  Sometimes  applied  specifi- 
cally to  the  chemical  activities  that  take  place  within 
cells. 

1.  Repair  and  growth  of  tissue. 

2.  Release  of  chemical  energy  in  the  form 

of  heat,  nervous,    and  muscular   ac- 
tivity. 

Enzymes. 

Oxygen. 

Internal  secretions. 

Anabolic  or  constructive  changes. 

Katabolic  or  destructive  changes. 

A.  Conversion  of  non-living  material  into 

protoplasm. 

B.  Oxidation,  including  neutralization  or 

elimination  of  acids. 

C.  Conversion  of  glucose  into  glycogen  and 
Consists  of  {  the   reconversion    of    glycogen    into 

glucose. 

D.  Conversion  of  glucose  into  fat. 

E.  Conversion  of  fat  into  glucose. 

F.  Conversion  of  amino-acids  to  glucose. 
.  G.    Conversion  of  amino-acids  to  fat. 


350 


ANATOMY  AND  PHYSIOLOGY     [CHAP.  XVI 


History 

Dependent 

upon 

Metabolism  of 

Carbohydrates 

Functions 

Waste          j 

Products  I 

Derange-     j 

ments  of  1 

1.  Supply  regulated  by  diet. 

2.  Storage    provided    for    temporarily    by 

liver,   muscles,   and   cells   of   tissues. 
Simple  sugars  stored  as  glycogen. 

3.  Consumption  controlled  by  the  energy 

needs  of  the  tissues. 

Control  of  nervous  system,  and  the  internal 
secretions  of  the  adrenals,  pancreas,  and 
hypophysis. 

Furnish  main  source  of  energy  for  muscular 
work  and  all  the  nutritive  processes. 

Help  to  maintain  the  body  temperature. 

Form  reserve  fund  for  time  of  need  (glyco- 
gen). 

Protect  the  body  tissues. 

Excess  carbohydrates  are  converted  into 
adipose  tissue. 

Carbon  dioxide. 

Water. 

1.  Interference  with  storage  of  glycogen. 

2.  Inability  to  oxidize  at  consumption  end. 


Metabolism  of 
Fats 


Reconstruction  —  In  act  of  passing  through  epithelial 
cells  of  villi,  glycerine  and  fatty  acids 
combine   to   form   fat   peculiar   to 
animal. 
Serve  as  fuel,  yield  heat  and  other  forms  of 

energy. 
Functions    {  Form  reserve  fund  for  time  of  need  (adipose 

tissue) . 

Act  as  protein  sparers. 
Waste          j  Carbon  dioxide. 

Products  1  Water. 

Derange-     j  Results  in  formation  of  compounds  of  an 
ments  of  I      acid  character  —  acidosis. 

Due  to  excessive  amounts  of  carbohydrates 
and  fats. 


Obesity 


Sedentary  life  and  absence  of  worry  are 
contributing  factors. 


CHAP.  XVI] 


SUMMARY 


351 


Absorbed  as  amino-acids,  carried  by  blood  to  all  the  cells 

of  the  body. 

1.  Build  up  tissue. 

Functions 

2.  Serve 

same  purpose  as   carbohydrates 

and  fats. 

Metabolism 

Adequate 

proteins  contain  all  the  materials 

of 

Nutritive 

for  maintenance  and  growth  of  tissue. 

Proteins 

Value 

Inadequate  proteins  serve  same  purpose  as 

carbohydrates  and  fats. 

Nitrogen 
Equilib- 

Condition  when   the   amount   of   protein 
nitrogen  taken  into  the  body  in  food  is 
equal  to  the  amount  eliminated  in  the 

rium 

excreta. 

Flavors 

Have  no 

nutritive  value,  but  increase  the 

and  Con- 

secretion of  eastric  fluid. 

diments 

Tea  —  stimulating  action  due  to  caffeine. 

Coffee  - 

stimulating  action  due  to  caffeine. 

Contains  carbohydrate,  fat,  and 

Croons 

protein. 

Stimulants 

V_yU^L/d 

Stimulating  effects  due  to  theo- 

bromin 

Accessory 

IVIeats 

Contain     secretogogues     which 

Articles 

Extract 

stimulate  the  gastric  glands  to 

of  Food 

secretion. 

Oxidized  rapidly,  yields  heat. 

Waste       i 

Carbon  dioxide. 

Products 

Water. 

Moderate  drinking  creates  keen 

Alcohol 

appetite,     and    thus    favors 

Favors 

overeating. 

Obesity 

Lessens  need  for  oxidation  of  fat 

or  carbohydrates,  hence  these 

are  spared  to  accumulate. 

Oxidation  changes  latent  energy  of  food  into  energy  of 

motion,  and  heat. 

Constant 

Temper- 
ature 

Supply  of  heat  needed  to  maintain  tem- 
perature, derived  from  oxidation. 

Energy  Value 

Unit  of  measurement  for  heat  production. 

of  Food 

Calorie 

Large  calorie  =  quantity  of  heat  necessary 

to  raise 

one  kilogram  of  water  1  degree 

centigrade. 

Carbohydrates  —  1  gm. 

=  4  cal. 

Fat  —                       1  gm. 

=  9  cal. 

Protein  —                1  gm. 

=  4  cal. 

352 


ANATOMY  AND  PHYSIOLOGY     [CHAP.  XVI 


Average 
Amount  of 
Food  Required 


Recommended 
Distribution 


Dependent  f  1.  Activity    3.  Size 
upon        1 2.  Age  4.  Sex 

About  40  calories  for  each  kilogram  of  body  weight. 

Cal. 

Carbohydrate          275  gm.  X4  =     1100 
Fat  100gm.X9=       900 

Protein  75gm.X4=       300 

Total       2300 

Undernutrition  —  lessens  natural  powers  of  resistance  to 
disease. 

1 .  Puts  unnecessary  strain  on  the  organs 

of  nutrition  and  excretion. 

2.  Favors  obesity. 

Overeating        ^  3.  Increases  amount  of  waste  products, 
toxic    material,    and   causes  flat- 
ulence. 
4.  Retards  secretion  of  gastric  juice. 


Vitamines 


Substances  essential  to  metabolism. 

Do  not  serve  as  source  of  energy  or  as  direct  building 

stones. 
Necessary  for  growth,  and  probably  to  prevent  such 

diseases  as  beriberi,  scurvy,  and  pellagra. 
Found  in  fresh  fruit  juices,  milk,  eggs,  bran  of  wheat,  rice, 

and  other  cereals. 


Ductless 
Glands 


Glandular  structures  that  possess  no  ducts. 

Produce  internal  secretions  that  are  carried  from  the 

gland  by  the  blood  or  lymph. 
Function  is  imperfectly  understood. 

The  Thyroid. 

The  Parathyroids. 

The  Thymus. 
Most  im-         The  Adrenals, 
portant       |  The  Hypophysis. 

The  Epiphysis. 

The  Testes. 

The  Ovaries. 


Thyroid 


Small  gland.     Weighs  about  one  ounce. 
Consists  of  two  lobes  connected  by  an  isthmus. 
Placed  in  front  of  trachea,  below  thyroid  cartilage. 
Function  not  definitely  known,  but  the  internal  secretion 

is  thought  to  be  necessary  for  the  continuance  of  normal 

metabolism. 


CHAP.  XVI] 


SUMMARY 


353 


Parathyroids 


Thymus  .     . 


Adrenals 


Hypophysis 


Epiphysis     . 


2A 


Four  small  masses,  each  about  j  in.  diameter. 

Two  are  embedded  in  each  lobe  of  thyroid. 

Consist  of  epithelioid  cells,  invested  with  areolar  tissue. 

Function  is  supposed  to  consist  in  neutralizing  toxic 
substances. 

Consists  of  two  large  masses  of  glandular  tissue  situated 
below  the  thyroid  and  in  front  of  the  trachea. 

Temporary  organ.  Attains  its  full  size  at  end  of  second 
year.  Then  ceases  to  grow,  remains  stationary  until 
puberty,  at  which  time  it  degenerates. 

Function  not  definitely  known,  but  it  is  thought  to  have 
a  definite  connection  with  growth  and  with  the  develop- 
ment of  the  reproductive  organs. 

Small  glands  lying  above  each  kidney.  Weigh  one  drachm. 

Consist  of  a  fibrous  framework,  the  spaces  of  which  are 
filled  with  groups  of  cells.  They  are  enclosed  in  a 
fibrous  capsule  and  are  well  supplied  with  blood- 
vessels, lymphatics,  and  nerves. 

Internal  secretion  —  adrenalin,  which  owes  its  power  to 
adrenin. 

1.  As  emergency  organs  in  times  of  emo- 
tional stress. 

Functions      ^  2.  To  postpone  fatigue. 

3.  Furnishes      seemingly      indispensable 
hormones. 

Small  reddish  gray  gland. 

Consists  of    f  dnterior  lo,b?' large  a,?d  glandular' 


two  lobes 


Functions 


I  Posterior  lobe,   small   and   composed   of 
[      nerve  tissue. 
Lodged  in  depression  of  the  sphenoid  bone. 

Anterior  lobe  furnishes  secretion  which 
stimulates  growth  of  skeleton,  possibly 
all  connective  tissues,  and  exerts  some 
essential  influence  on  metabolism. 
Posterior  lobe  furnishes  several  hormones 
which  have  a  stimulating  effect  on  tone 
of  plain  muscle,  secretory  activity  of 
several  glands,  glycogenolysis,  etc. 
Small  reddish  gray  body  located  in  the  third  ventricle 
of  the  brain.  Glandular  organ;  attains  maximum 
growth  about  seventh  year.  From  this  period  and 
particularly  after  puberty  it  decreases  in  size  and  be- 
comes fibrous. 

Function  not  definitely  known;  it  is  thought  to  inhibit 
growth  and  restrain  the  development  of  the  reproduc- 
tive organs. 


354 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVI 


Spleen 


Descrip- 


tion 


Functions 


Beneath  diaphragm,  behind  and  to  the  left 

of  the  stomach. 
Consists  of  a  fibrous  network  filled  with  a 

vascular  pulp,  enclosed  in  a  fibrous  and 

muscular  capsule  which  is  covered  by 

serous  membrane. 
Blood  supply  peculiar  —  arteries  —  veins, 

no  connecting  capillaries. 
Not  definitely  known.     Credited  with  the 

following :  — 

1.  Formation   of  red   cells   during  foetal 

life  and  for  short  period  after  birth. 

2.  Helps  in   preparation   of  new  haBmo- 

globin  or  preservation  of  iron  set  free 
by  death  of  red  cells. 

3.  May  assist  in  digestion  and  metabolism. 

4.  May  assist  in  production  of  uric  acid. 

5.  May  protect  body  from  infections. 


CHAPTER  XVII 


WASTE  PRODUCTS  ;    EXCRETORY  ORGANS  ;  DESCRIPTION  OF  THE 
ORGANS   CONSTITUTING   THE   URINARY   SYSTEM;   URINE 

IN  the  previous  chapters  we  have  seen  that  the  blood  is  con- 
stantly supplied  by  means  of  the  respiratory  and  digestive  mecha- 
nisms with  all  the  chemical  substances  it  requires  to  maintain  the 
life,  growth,  and  activity  of  the  body.  These  substances,  enter- 
ing the  current  of  the  blood,  are  carried  to  all  the  cells  and  are  in- 
cessantly combining  with  the  chemical  substances  of  which  these 
cells  are  composed.  One  of  the  results  of  these  chemical  com- 
binations is  the  formation  of  waste  products,  which  must  be 
removed  from  the  body,  as  many  of  them  are  toxic. 

WASTE  PRODUCTS 
The  wastes  of  cell  metabolism  may  be  listed  as  follows :  — 

Q  i  KI    G  u   I  Nitrogenous  salts,  e.g.,  urea. 

1.  Soluble  halts  \  r  ,  ,.         , .    . , 

[  Inorganic  salts,  e.g.,  sodium  chloride. 

2.  Liquid  —  Water. 

3.  Gas  —  Carbon  dioxide. 

4.  Solids  —  Waste  materials  from  food. 

These  wastes  are  classed  as  excreta  and  the  process  by  which  they 
are  removed  from  the  body  as  excretion  or  elimination. 

EXCRETORY  ORGANS 

The  organs  that  function  as  excretory  organs  and  the  products 
that  they  eliminate  may  be  tabulated  as  follows :  - 


ESSENTIAL 

INCIDENTAL 

Lungs   .... 

Kidneys    .     .     . 

Alimentary  canal 

Carbon  dioxide 
Water  and  soluble  salts, 
resulting  from  metabo- 
lism of  proteins,  neutral- 
ization of  acids,  etc. 
Solids 

Water 
Carbon  dioxide  and  solids. 

Water,  carbon  dioxide,  and 
salts. 

355 


356 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVII 


KIDNEV 


In  this  chapter  we  devote  ourselves  to  the  consideration  of  the 
urinary  system,  which  includes  the  following  organs :  - 

Kidneys,  which  form 
the  urine  from  mate- 
rials taken  from  the 
blood. 

Ureters,  ducts  which 
convey  the  urine  away 
from  the  kidneys. 

1  Bladder,  a  reser- 
voir for  the  reception 
of  urine. 

Urethra,  a  tube 
through  which  the 
urine  passes  from  the 
bladder  and  is  finally 
voided. 

KIDNEYS 

The  kidneys  are  two 
compound  tubular 
glands,  placed  at  the 
back  of  the  abdominal 
cavity,  one  on  each 
side  of  the  spinal 
column  and  behind  the 

peritoneal  cavity.  They  correspond  in  position  to  the  space 
included  between  the  upper  border  of  the  twelfth  thoracic 
and  the  third  lumbar  vertebra.  The  right  is  a  little  lower 
than  the  left  in  consequence  of  the  large  space  occupied  by  the 
liver. 

Capsule  and  supports.  —  The  kidneys  are  covered  by  a  thin 
but  rather  tough  envelope  of  fibrous  tissue  called  the  capsule, 
the  inner  surface  of  which  is  slightly  attached  to  the  substance  of 
the  kidney  by  means  of  fine  fibres  and  blood-vessels.  The  kidneys 
are  usually  embedded  in  a  mass  of  fatty  tissue  termed  the  peri- 
renal  fat,  and  are  not  held  in  place  by  any  distinct  ligaments, 
but  rather  by  the  pressure  and  counter-pressure  exerted  upon 
them  by  neighboring  structures. 


BLADDER 


URETHRA 


FIG.  182.  —  THE'  URINARY  SYSTEM  VIEWED  FROM 
BEHIND. 


CHAP.  XVII] 


URINARY  SYSTEM 


357 


Size  and  shape.  —  Each  kidney  is  about  four  and  one-half 
inches  (11.2  cm.)  long,  two  and  one-half  inches  (6.2  cm.)  broad, 
one  and  one-half  inches  (3.7  cm.)  thick,  and  weighs  about  four  and 
one-half  ounces  (135  gm.).  They  are  bean  shaped,  with  the  con- 
cave side  turned  toward  the  spine,  and  the  convex  side  directed 
outward.  Near  the  centre  of  the  concave  side  is  a  depression 
called  the  hilum,  which  serves  as  a  passageway  for  the  ureter, 


PYRAMIDS 


CORTEX 


MEDULLA — g 


COLUMNS  OF 
BERTINI 


—  URETER 


RENAL 
ARTERr 


FIG.  183.  —  LONGITUDINAL  SECTION  OF  THE  HUMAN  KIDNEY.     (Modified 

from  Huxley.) 

and  for  the  blood-vessels,  lymph-vessels,  and  nerves  going  to  and 
from  the  kidney. 

Anatomy  of  the  kidney.  —  If  a  kidney  is  cut  in  two  lengthwise, 
it  is  seen  that  the  upper  end  of  the  ureter  expands  into  a  basin- 
like  cavity,  called  the  pelvis  of  the  kidney.  This  pelvis  is  irregu- 
larly subdivided  into  smaller,  cup-like  cavities,  called  calyces, 
which  receive  the  pointed  projections  of  the  kidney  substance. 

The  substance  of  the  kidney  is  readily  seen  by  the  naked  eye 
to  consist  of  two  distinct  parts  :  (1)  an  outer,  and  more  solid  por- 
tion, called  the  cortex  (bark) ;  and  (2)  an  inner,  striated  portion, 
called  the  medulla  (marrow),  which  is  not  a  solid  mass,  but  more 
or  less  distinctly  divided  into  pyramidal-shaped  sections.  The 
cortical  substance  penetrates  for  a  variable  distance  between  the 


358 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XVII 


pyramids,  separating  and  supporting  them.  These  inter-pyram- 
idal extensions  are  called  the  columns  of  Bertini  and  support  the 
blood-vessels.  The  pointed  projections,  or  papilla,  of  the  pyramids 
are  received  by  the  cup-like  cavities  or  calyces  of  the  pelvis.  The 
bulk  of  the  kidney  substance,  both  in  the  cortex  and  medulla,  is 
composed  of  little  tubes  or  tubules,  closely  packed  together,  having 


CAPSULE 


PROXIMAL 
CONVOLUTED  TUBE 


"—CAPSULE 

AM 

V PROXIMAL 

CONVOLUTED  TUBE 


COLLECTING  TUBE 


LOOP  OF  HENLE 


EXCRETORY  TUBE 
FIG.  184.  —  DIAGRAM  OF  THE  COURSE  OF  Two  URINIFEROUS  TUBULES. 

only  just  enough  connective  tissue  to  carry  a  large  supply  of 
blood-vessels  and  a  certain  number  of  lymphatics  and  nerves. 

Uriniferous  tubules.  —  Examined  under  the  microscope,  it  is 
seen  that  the  uriniferous  tubules  begin  as  little  hollow  globes,  called 
capsules,  in  the  cortex  of  the  kidney.  These  capsules  are  joined 
to  the  tubules  by  a  constricted  neck,  and  the  tubules,  after  running 
a  very  irregular  course,  open  into  straight  collecting  tubes,  which 


FIG.  185.  —  DIAGRAM  OF  THE  STRUCTURE  or  A  LOBE  OF  THE  KIDNEY.  The  lobe 
is  seen  in  vertical  section,  the  cortex  being  marked  off  from  the  medulla.  Four 
medullary  rays  encroach  upon  the  cortex.  At  the  left  is  shown  the  course  of  a  single 
continuous  series  of  tubes  —  the  straight  and  spiral  tubes  appearing  in  the  medul- 
lary ray;  the  straight,  looped,  and  excretory  in  the  medulla  proper;  the  capsule, 
neck,  convoluted,  irregular,  and  arched  in  the  cortex  proper.  Next  is  seen  the 
labyrinth,  composed  of  a  mass  of  tubes  in  the  cortex,  with  a  medullary  ray  for  a 
centre.  Equidistant  from  the  ray  on  each  side  is  a  broken  red  line,  marking  the 
position  of  an  interlobular  artery.  The  parts  between  these  lines  constitute  a 
lobule.  Farther  to  the  right  is  an  interlobular  artery,  giving  off  lateral  branches 
(afferent  vessels),  each  of  which  ends  in  a  tuft  of  capillaries,  from  which  the  blood 
is  collected  by  an  efferent  vessel.  The  uppermost  of  the  tufts  is  shown  enclosed  in 
a  capsule.  On  the  right  of  the  interlobular  artery  the  efferent  vessels  break  up 
into  a  capillary  network  which  surrounds  the  (unrepresented)  tubes  in  the  cortex 
and  ray.  The  lowest  efferent  sends  vertical  vessels  also  into  the  medulla.  On 
the  right  the  interlobular  vein  is  seen  gathering  the  blood  from  all  the  parts  supplied 
by  the  interlobular  artery.  A  branch  of  the  renal  artery  courses  upward  between 
cortex  and  medulla,  and  forms  an  arch  (here  broken)  over  the  base  of  the  medulla. 
From  it  the  interlobular  arteries  pass  upward  into  the  cortex,  and  straight  branches 
go  downward  into  the  medulla,  supplying  its  structure,  and  ending  at  the  apex 
in  the  capillaries.  From  the  last  the  radicles  of  the  renal  vein  arise,  and  accompany 
the  straight  arteries  to  the  base  of  the  medulla,  where  a  venous  arch  is  formed, 
continuous  with  which  is  the  vena  comes  of  the  entering  artery.  The  calyx  embraces 
the  apex  of  the  medullary  pyramid.  It  is  lined  with  epithelium,  which  continues 
from  it  over  the  apex,  the  latter  being  perforated  with  the  many  apertures  of 
excretory  tubes.  (Gerrish.) 

359 


360 


ANATOMY  AND  PHYSIOLOGY    [CHAP.  XVII 


pour  their  contents  through  their  openings  in  the  pointed  ends  or 
papillae  of  the  pyramids,  into  the  calyces  of  the  kidney. 

The  tubules  are  composed  of  basement  membrane,  lined  through- 
out by  epithelial  cells.  The  cells  vary  in  the  different  parts  of  a 
tubule,  those  of  the  capsule  and  convoluted  or  irregular  parts 
being  more  especially  adapted  to  secretory  purposes  than  the 
straight  parts  of  the  tubule. 


RENAL    OR 
MALPIGHIAN  CORPUSCLES 


URINIFEROUS 
TUBULE 


PLEXUS 


FIG.  186.  —  PLAN  OF  THE  BLOOD-VESSELS  CONNECTED  WITH  THE  TUBULES. 

Pyramid.  —  These  collecting  tubules  en  masse,  together  with 
interstitial  tissue,  blood-vessels,  and  lymphatics,  make  a  pyramid. 
The  number  of  pyramids  varies. 

Renal  or  Malpighian  corpuscles.  —  In  the  cortical  portion  of  the 
kidney  are  found  renal  corpuscles  which  consist  of  two  parts  :  (1)  a 
minute  tuft  of  capillaries  called  a  glomerulus,  surrounded  by  (2) 
a  closed  capsule  which  is  the  beginning  of  a  uriniferous  tubule. 
The  investment  of  the  glomerulus  by  the  capsule  is  double  and 


CHAP.  XVII]  URINARY   SYSTEM  361 

complete  except  at  one  point,  where  an  afferent  vessel  enters  and 
an  efferent  vessel  leaves. 

The  blood  supply  of  the  kidney.  —  For  its  size,  the  kidney  is 
abundantly  supplied  with  blood.  The  renal  artery,  coming  di- 
rectly from  the  aorta,  divides,  before  it  enters  the  hilus  of  the  kid- 
ney, into  several  branches,  which  pass  into  the  tissue  of  the  organ. 
Branches  from  these  arteries  have  two  destinations :  (1)  into  the 
cortex,  and  (2)  into  the  pyramids. 

(1)  When  the  arteries  reach  the  level  of  the  base  of  the  pyra- 
mid, the  branches  divide  laterally  to  form  more  or  less  complete 
arches   between   the    cortex   and    medulla.     From    the   arterial 
arches,   vessels  pass  upward  through  the  cortex  (interlobular), 
giving  off  at  intervals  tiny  arteries,  each  of  which  enters  1  the 
dilated  commencement  or  capsule  of  a  uriniferous  tubule.     These 
tiny  arteries,  entering  the  capsule,  are  spoken  of  as  afferent  vessels. 
They  push  the  thin  walls  of  the  capsule  before  them,  break  up  into 
a  knot  of  capillary  vessels,  called  a  glomerulus,  and  finally  issue 
from  the  capsule  as  efferent  vessels,  near  the  point  at  which  the 
afferent  vessel  entered.     These  efferent  vessels  are  much  smaller 
than  the  afferent  vessels.     They  do  not  immediately  join  to  form 
veins,  but  break  up  into  a  close  meshwork  or  plexus  of  capillaries 
around  the  tubules,  before  they  unite  to  form  the  larger  vessels 
and  pour  their  contents  into  the  veins.     These  veins  terminate  in 
venous  arches  between  the  cortex  and  medulla.     It  is  in  this  way 
that  the  cortex  is  supplied  with  blood. 

(2)  The  pyramids  also  receive  their  blood  supply  from  the  ar- 
terial arches.     The  blood  passes  downward  in  straight  vessels  be- 
tween the  uriniferous  tubules,  to  be  returned  by  more  or  less 
straight  veins  to  the  venous  arches,  whence  it  is  conveyed  by  large 
branches  into  the  renal  vein,  which  leaves  the  kidney  at  the  hilus 
and  pours  its  contents  into  the  inferior  vena  cava. 

It  is  worthy  of  note  that,  unlike  the  lungs  and  the  liver,  the 
kidney  receives  blood  from  just  one  artery,  and  this  blood  distrib- 
uted in  different  sets  of  vessels  serves  the  purposes  of  nourishment 
for  the  kidney  substance,  and  the  purposes  of  excretion.  It  is 
from  the  capillaries  of  the  glomeruli  and  the  plexus  of  capil- 

1  The  artery  does  not  penetrate  the  wall  of  the  capsule,  but  the  knot  of  capillary 
vessels  is  contained  within  the  capsule,  as  the  heart  is  contained  within  the  peri- 
cardium. 


362  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVII 

laries  around  the  convoluted  portion  of  the  tubules,  that  the 
passage  of  waste  material  from  the  blood  into  the  tubule  takes 
place.  Other  capillaries  serve  to  hold  the  blood  that  is  used  for 
nourishment. 

Nerves  and  lymphatics.  —  The  kidneys  are  well  supplied  with 
nerves  derived  from  both  the  sympathetic  and  central  nervous 
systems.  Many  of  these  nerves  are  vasomotor  nerves,  and  by  regu- 
lating the  contraction  and  dilatation  of  the  blood-vessels,  they 
influence  the  blood  pressure  in  the  kidneys.  They  are  also  well 
supplied  with  lymphatics. 

Function  of  the  kidneys.  —  The  function  of  the  kidneys  is  to 
separate  waste  matters  (urine)  from  the  blood,  and  thus  help  to 
maintain  its  normal  composition.  The  waste  matters  are  those 
resulting  from  metabolism,  particularly  of  proteins;  water,  salts, 
and  foreign  matters  such  as  toxins,  whether  formed  in  the  body, 
or  taken  into  the  body  from  outside.  The  concentration  of  urine, 
and  not  the  quantity,  is  our  criterion  for  judging  the  amount  of 
work  done  by  the  kidneys.  It  is  probable  that  they  are  most 
severely  taxed  when  they  have  to  remove  from  the  blood  a 
maximum  of  dissolved  solids  in  a  minimum  of  water. 

The  secretion  of  urine.  —  The  exact  way  in  which  the  kidneys 
separate  the  urine  from  the  blood  is  not  known,  but  it  is  thought 
to  be  a  double  process,  being  partially  accomplished  by  a  mechani- 
cal filtration  and  partially  by  secretion  due  to  the  selective  action 
of  the  cells  lining  the  tubules. 

(1)  Into  each  hollow  capsule  which  forms  the  beginning  of  a 
uriniferous  tubule  an  afferent  artery  enters.  This  artery  breaks 
up  into  capillaries  which  form  a  bunch  of  looped  and  twisted 
blood-vessels  called  a  glomerulus.  The  walls  of  the  capsule  being 
double,  the  glomerulus  pushes  back  the  inner  wall  or  visceral 
layer,  until  the  capsule  is  entirely  filled,  leaving  only  a  small  space 
between  it  and  the  outer  wall  or  parietal  layer.  The  blood  in  the 
glomerulus  is  only  separated  from  the  interior  of  the  tubule  by 
the  thin  walls  of  the  capillaries  and  the  inverted  wall  of  the  cap- 
sule. The  artery  (afferent)  which  enters  the  capsule  is  larger 
than  the  issuing  (efferent)  vessel,  and  during  its  passage  through 
the  glomerulus,  the  blood  is  subjected  to  considerable  pressure. 
As  a  result  of  this,  a  transudation  of  the  watery  constituents  of 
the  blood,  with  some  dissolved  salts,  takes  place  through  the 


CHAP.  XVII]  URINARY   SYSTEM  363 

walls  of  the  blood-vessels  and  the  walls  of  the  capsule  into  the 
capsular  space,  then  into  the  tubule. 

(2)  After  leaving  the  capsule,  the  efferent  vessel  communicates 
with  other  similar  vessels,  which  together  form  a  meshwork  or 
plexus  of  capillaries  closely  surrounding  the  tubules,  so  that  the 
blood  is  again  brought  into  close  communication  with  the  in- 
terior of  the  tubules.  The  tubules  are  lined  with  secreting  cells, 
and  these  cells  appear  to  have  the  power  of  selecting  from  the 
blood  the  more  solid  waste  matters  (especially  the  urea),  which 
fail  to  filter  through  the  flat  cells  forming  the  wall  of  the  capsule. 

THE  URETERS 

The  ureters  are  the  excretory  ducts  of  the  kidneys.  They 
consist  of  a  distended  portion  called  the  pelvis,  which  is  contained 
within  the  kidney,  and  a  duct.  Each 
duct  is  about  the  diameter  of  a  goose- 
quill,  and  from  ten  to  twelve  inches 
(25  to  30  cm.)  long.  They  consist 
of  three  coats  :  an  outer  fibrous  coat, 
a  middle  muscular,  and  an  inner 
mucous  lining  which  is  continuous 
above  with  that  of  the  pelvis  of  the 
kidney,  and  below  with  that  of  the 

bladder.  FIG.    187.  —  DIAGRAM    SHO\\- 

.—.,  ING    METHOD   OF   ENTRANCE    OF 

Function.  —  The     Ureters    connect     THE  URETER  INTO  THE  BLADDER. 

the   kidneys  with   the  bladder  and     (Gerrish.) 

serve  as  a  passageway  to  convey  urine  from  the  kidneys  to  the 

bladder. 

BLADDER 

The  bladder  is  a  hollow  muscular  organ  situated  in  the  pelvic 
cavity  behind  the  pubes,  in  front  of  the  rectum  in  the  male,  and  in 
front  of  the  anterior  wall  of  the  vagina,  and  the  neck  of  the  uterus, 
in  the  female.  It  is  a  freely  movable  organ,  but  is  held  in  position 
by  ligaments.  During  infancy  it  is  conical  in  shape  and  projects 
above  the  upper  border  of  the  pubes  into  the  hypogastric  region. 
In  the  adult,  when  quite  empty,  it  is  placed  deeply  in  the  pelvis ; 
when  slightly  distended,  it  has  a  round  form ;  but  when  greatly 
distended,  it  is  ovoid  in  shape  and  rises  to  a  considerable  height 
hi  the  abdominal  cavity.  It  is  customary  to  speak  of  the  widest 


364  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XVII 

part  as  the  fundus,  and  the  part  where  the  bladder  becomes 
continuous  with  the  urethra  as  the  neck,  or  cervix.  It  has  four 
coats :  — 

1.  The  serous  coat  is  a  reflection  of  the  peritoneum,  and  only 
covers  the  upper  portion  of  the  fundus. 

2.  The  muscular  coat  has  three  layers,  an  inner  longitudinal, 
middle  circular,  and  outer  longitudinal.    The  circular  fibres  are 
collected  into  a  layer  of  some  thickness  around  the  cervix  or  neck, 
where  the  bladder  becomes  continuous  with  the  urethra.     These 
circular  fibres  around  the  neck  form  a  sphincter  muscle  which  is 
normally  in  a  state  of  contraction,  only  relaxing  at  intervals,  when 
the  accumulation  of  urine  within  the  bladder  renders  its  expulsion 
necessary. 

3.  The  areolar  coat  connects  the  mucous  and  muscular. 

4.  The  mucous  membrane  lining  the  bladder  is  continuous  with 
that  of  the  ureters  and  the  urethra. 

Function.  —  The  bladder  serves  as  a  reservoir  for  the  reception 
of  urine.  When  moderately  distended,  it  holds  about  one  pint 
(about  one-half  litre). 

THE  URETHRA 

The  urethra  is  a  narrow,  membranous  canal,  about  an  inch 
and  a  half  (3.8  cm.)  in  length  in  the  female.  Its  normal  diameter 
is  about  one-quarter  of  an  inch  (6.3  mm.),  but  it  admits  of  consid- 
erable dilatation.  It  extends  from  the  neck  of  the  bladder  to  the 
external  orifice,  which  is  named  the  meatus  urinarius.  It  is  placed 
behind  the  symphysis  pubis,  and  is  embedded  in  the  anterior  wall 
of  the  vagina.  Its  direction  is  obliquely  downward  and  forward, 
its  course  being  slightly  curved,  with  the  concavity  directed  for- 
ward and  upward.  Its  external  orifice  is  the  narrowest  part  and 
is  located  between  the  clitoris  and  the  opening  of  the  vagina.  (See 
Fig.  222.) 

The  wall  of  the  urethra  consists  of  three  coats,  an  outer  muscular 
coat,  a  submucous  coat,  and  an  inner  mucous  coat  which  is  con- 
tinuous with  that  of  the  bladder. 

MICTURITION 

Urine  is  secreted  continuously  by  the  kidneys.  It  is  carried 
to  the  bladder  by  the  ureters,  and  at  intervals  is  expelled  from  the 


CHAP.  XVII]  WASTE  PRODUCTS  365 

bladder  through  the  urethra.  The  act  by  which  the  urine  is  ex- 
pelled is  called  micturition.  It  occurs  normally  as  the  result  of 
irritation  due  to  the  accumulation  of  urine  within  the  bladder. 
The  accumulation  stimulates  the  muscular  walls  to  contract,  and 
the  resistance  of  the  sphincter  at  the  neck  of  the  bladder  is  over- 
come. The  action  is  involuntary,  but  it  may  be  controlled  by 
voluntary  effort. 

Involuntary  micturition.  —  Involuntary  micturition  may  occur 
as  the  result  of  lack  of  consciousness,  and  as  the  result  of  spinal 
injury  involving  the  nerve  centres  which  send  nerves  of  control 
to  the  bladder.  It  may  be  due  to  a  want  of  tone  in  the  muscu- 
lar walls,  or  it  may  result  from  some  abnormal  irritation. 

Retention  of  urine.  —  Retention  or  failure  to  void  urine  may 
be  due  to :  (1)  dulling  of  the  senses  so  that  there  is  no  desire  to 
void,  (2)  nervous  contraction  of  the  urethra,  and  (3)  some  ob- 
struction in  the  urethra  or  in  the  neck  of  the  bladder. 

In  some  cases  the  bladder  may  become  so  fully  distended  that 
the  retention  of  urine  may  be  accompanied  by  more  or  less  con- 
stant voiding  of  small  amounts  of  urine. 

Suppression  of  urine.  —  A  far  more  serious  condition  than  re- 
tention is  the  failure  of  the  kidneys  to  secrete  urine.  This  is 
spoken  of  as  suppression,  and  is  usually  due  to  extreme  conges- 
tion of  the  kidneys,  as  in  acute  nephritis. 

THE    URINE 

Normal  urine  may  be  described  as  a  transparent,  amber-colored 
liquid,  with  a  characteristic  odor,  an  acid  reaction  when  tested 
with  litmus  paper,  and  a  specific  gravity  of  about  1.020. 

Transparency.  —  The  transparency  of  urine  may  be  diminished 
in  health  by  the  presence  of  mucus,  derived  from  the  genito- 
urinary tract,  or  by  the  deposit  of  salts.  In  disease  the  urine  may 
become  clouded  by  the  presence  of  pus. 

Color.  —  The  color  of  urine  depends  upon  the  quantity  voided 
and  the  relative  amounts  of  water  and  coloring  matters.  If  the 
quantity  is  abnormally  increased,  it  is  usually  more  dilute  and  of 
a  paler  color ;  as,  for  instance,  the  copious  light-colored  urine  of 
hysteria  or  diabetes  insipidus.  One  exception  to  this  is  diabetes 
mellitus,  where  the  quantity  is  increased,  but  the  color  is  dark 


366  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVII 

because  of  the  presence  of  sugar.  When  the  quantity  is  diminished 
as  in  fevers,  it  is  generally  highly  colored,  because  the  amount  of 
solids  present  is  large.  Other  causes  of  change  of  color  are  the 
presence  of  abnormal  substances,  and  large  doses  of  certain  drugs. 

Reaction.  —  The  reaction  of  human  urine  is  largely  dependent 
on  the  kind  of  food  eaten.  Many  of  the  waste  products  that 
result  from  a  mixed  diet  are  acid,  hence  the  reaction  of  human 
urine  is  usually  acid.  On  a  diet  of  vegetables  the  urine  will  be 
alkaline,  as  it  is  with  herbivorous  animals.  If  human  urine  is 
allowed  to  stand  for  any  length  of  time,  it  will  become  alkaline, 
because  bacteria  will  decompose  the  protein  constituents  into 
ammonia  and  other  alkalies.  In  certain  diseased  conditions  of 
the  urinary  organs  this  same  process  takes  place  within  the 
body. 

Specific  gravity.  —  The  specific  gravity  depends  upon  the 
amount  of  solid  waste  matters  present  in  the  urine.  In  health, 
it  may  vary  from  1.010  to  1.030.  When  the  solids  are  dissolved 
in  a  large  amount  of  water,  the  specific  gravity  will  naturally  be 
lower  than  when  the  urine  is  more  concentrated.  A  high  specific 
gravity  denotes  the  presence  of  abnormal  constituents;  as,  for 
instance,  the  specific  gravity  is  notably  heightened  by  the  presence 
of  sugar  in  diabetes  mellitus. 

Quantity.  —  The  average  quantity  of  urine  secreted  in  twenty- 
four  hours  by  a  healthy  adult  is  from  forty  to  fifty  ounces  (1.2  to 
1.5  litres).  A  child  voids  relatively  more  urine  than  an  adult, 
but  absolutely  it  voids  less. 

From  2-5  years,  16-24  ounces  (480-720  cc.). 
From  5-8  years,  24-32  ounces  (720-960  cc.). 
From  9-16  years,  32-40  ounces  (960-1200  cc.). 

The  quantity  of  urine  may  be  increased  by  (1)  the  ingestion  of 
a  large  amount  of  liquid,  (2)  the  action  of  diuretics,  (3)  nervous- 
ness, (4)  certain  diseases  such  as  diabetes  insipidus,  diabetes 
mellitus,  and  hysteria. 

The  quantity  of  urine  may  be  decreased  by  (1)  the  ingestion  of 
a  small  amount  of  liquid,  (2)  vomiting,  (3)  diarrhoea,  (4)  high 
fever,  (5)  disease  of  the  kidneys,  and  (6)  the  action  of  diapho- 
retics, muscular  activity,  or  any  treatment  that  induces  free  per- 
spiration. 


CHAP.  XVII] 


WASTE   PRODUCTS 


367 


COMPOSITION   OF  URINE 

The  composition  of  urine  is  very  complex;  even  in  health 
it  varies,  depending  on  the  quantity  and  kind  of  food  eaten,  etc. 
It  is  not  difficult  to  understand  this  complexity  when  one  recalls 
that  the  kidneys  eliminate  some  of  all  the  end-products  resulting 
from  food  metabolism,  together  with  the  products  of  bacterial 
fermentation  in  the  stomach  and  intestines.  Under  pathological 
conditions  the  composition  may  be  still  further  modified.  It  is 
not  possible  to  describe  all  the  numerous  constituents  here.  A  few 
are  as  follows  :  — 


Urine 


Water, 

95  per  cent 

Urea  (2  per  cent  of  total  solids). 

Uric  acid. 

Purin  bodies 

Xanthin. 

Organic, 
about  3.7 

Creatinin. 

Hypoxanthin. 

Hippuric  acid. 

Other  substances. 

Soluble  salts   < 
5  per  cent 

Sodium  chloride. 

Sulphates. 

Phosphates. 

Inorganic, 

Potassium. 

i 

about  1.3 

Ammonium. 
Magnesium. 

Salts  of 

. 

Calcium. 

Other  substances. 

Urea.  —  Urea  constitutes  about  one-half  of  the  solid  constitu- 
ents of  the  urine,  and  represents  the  chief  end-product  resulting 
from  the  metabolism  of  the  proteins  of  the  food  and  tissues.  The 
result  of  the  oxidation  of  protein  material  exists  in  the  blood  until 
it  reaches  the  liver.  Under  the  action  of  the  liver  cells  this 
material  is  converted  into  urea.  About  0.028  per  cent  of  urea 
is  present  normally  in  the  blood  and  tissues.  The  kidneys 
constantly  remove  urea  as  it  is  formed,  and  by  their  activity 
keep  the  amount  of  urea  in  the  blood  at  the  low  level  given 
above.  If,  for  any  reason,  the  kidneys  fail  to  eliminate  urea, 
the  accumulation  in  the  blood  and  tissues  leads  to  a  condition 
of  poisoning. 

Normally  an  adult  voids  about  one  ounce  (30  gms.)  of  urea  in 


368  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVII 

twenty-four  hours,  but  the  quantity  is  increased  by  a  diet  rich  in 
proteins,  strenuous  exercise,  hot  baths,  fever  in  its  early  stages, 
and  some  diseases.  A  small  amount  of  protein  food,  excessive 
vomiting,  free  perspiration,  and  diseases  that  interfere  with 
elimination  will  decrease  the  amount  of  urea  voided. 

Purin  bodies.  —  In  the  classification  of  proteins  given  on  page 
309  nucleoproteins  are  listed.  These  are  compounds  of  protein 
with  a  complex  organic  acid  called  nucleic  acid,  which  contains 
phosphorus.  They  are  found  in  the  nuclei  and  protoplasm  of 
body  cells,  also  in  various  protein  foods.  When  nucleoproteins 
either  of  the  food  or  tissues  are  oxidized  in  the  body,  they  give 
rise  to  purin  bodies,  i.e.,  uric  acid,  xanthin,  and  hypoxanthin. 
Uric  acid  is  the  most  important,  and  next  to  urea  is  the  medium 
by  which  nitrogen  is  eliminated  from  the  body.  Uric  acid  com- 
bines with  potassium  and  sodium  to  form  urates,  and  is  found  in 
the  form  of  urates  in  the  urine.  In  gout  the  excretion  of  urates 
is  decreased,  and  it  accumulates  in  the  blood  and  is  deposited  in 
the  joints  in  the  form  of  insoluble  salts.  In  this  and  similar  con- 
ditions purin-free  diets,  i.e.,  diets  free  from  nucleoproteins,  are 
prescribed. 

Creatinin.  —  Creatinin  occurs  in  the  urine  constantly.  Its 
physiological  history  is  imperfectly  known.  Under  normal  con- 
ditions the  amount  of  creatinin  formed  in  the  body  is  independent 
of  the  proteins  eaten.  This  has  led  some  observers  to  think  that 
it  represents  an  end-product  of  the  metabolism  of  protein  tissue. 

Creatin  l  is  found  in  the  muscles,  liver,  heart,  brain,  and  other 
organs.  Nothing  definite  is  known  of  the  function  of  creatin,  but 
it  is  probable  that  from  it  the  creatinin  of  the  urine  is  formed. 
Creatin  is  absent  from  normal  urine,  but  is  present  in  the  urine 
during  starvation,  in  acute  fevers,  and  in  conditions  where  there  is 
a  rapid  loss  of  muscular  tissue. 

Hippuric  acid.  —  Hippuric  acid  represents  one  of  the  chemical 
methods  of  defence  of  the  organism  against  toxic  substances. 
The  amount  found  in  the  urine  varies  with  the  diet.  On 
a  diet  containing  much  fruit  and  vegetables  the  amount  ex- 
creted is  increased.  As  a  result  of  the  digestion,  fermentation 


1  The  formula  for  creatin  is  C 
The  formula  for  creatinin  is  C4H;NsO. 
The  difference  is  H2O.     Creatinin  is  the  anhydride  of  creatin. 


CHAP.  XVII]  WASTE   PRODUCTS  369 

by  bacteria,  or  oxidation  of  fruits  and  vegetables,  certain  toxic 
acids  are  formed,  e.g.,  benzoic  acid.  This  is  rendered  less  toxic 
by  combining  it  with  glycocoll  to  form  hippuric  acid  which  the 
kidneys  excrete. 

Salts.  —  The  salts  found  in  the  blood  are  derived  partly  from 
the  food  eaten,  and  partly  from  the  metabolism  of  proteins,  par- 
ticularly the  neutralization  of  acids.  Sodium  chloride  is  the  most 
abundant,  and,  next  to  urea,  is  the  chief  solid  found  in  urine.  In 
certain  inflammatory  conditions,  coupled  with  serous  exudate, 
e.g.,  pneumonia,  the  amount  of  sodium  chloride  excreted  is  very 
much  diminished. 

Abnormal  constituents.  —  The  chief  abnormal  constituents 
that  are  liable  to  appear  in  the  urine  are  albumin,  glucose,  indican, 
acetone,  casts,  calculi,  pus,  and  blood. 

Albumin.  —  Normally  the  kidney  cells  do  not  allow  albumin  to 
pass  into  the  tubules,  but  a  condition  of  temporary  albuminuria 
may  follow  overeating  or  severe  muscular  exercise.  In  abnormal 
conditions  of  the  kidneys  associated  with  nephritis  and  acute 
fevers,  albumin  is  usually  found  in  the  urine.  In  cases  of  heart 
disease,  where  the  blood-vessels  of  the  kidneys  are  subjected  to  ab- 
normal pressure  changes,  albumin  is  usually  present  in  the  urine. 

Glucose.  —  Normal  urine  contains  no  sugar,  or  so  little  that 
for  clinical  purposes  it  may  be  considered  absent.  In  health  the 
amount  of  glucose  present  in  the  blood  varies  from  0.1  to  0.15  per 
cent.  A  higher  per  cent  is  irritating  to  the  tissues,  so  when  the 
quantity  of  sugar  eaten  is  greater  than  the  system  can  promptly 
change  to  glycogen  and  fat,  the  kidneys  secrete  and  excrete  it. 
When  glucose  is  found  in  the  urine  from  this  cause,  it  is  called 
temporary  glycosuria.  Temporary  glycosuria  frequently  follows 
an  injury  to  the  head,  or  occurs  during  convalescence  from  fevers. 
In  these  cases  it  is  thought  to  be  due  to  temporary  inability  of 
the  system  to  oxidize  sugar.  In  the  disease  called  diabetes  mel- 
litus,  glucose  persists  in  the  urine.  In  mild  cases  this  condition 
can  be  controlled  by  lessening  the  amount  of  carbohydrate  food, 
but  in  severe  cases  glucose  will  appear  in  the  urine  even  when  no 
carbohydrates  are  eaten.  This  condition  is  serious  because  it 
means  that  the  body  tissues  are  being  oxidized  to  form  glucose. 

Indican.  —  Indican  is  a  potassium  salt  that  is  formed  from 
indol.  Indol  results  from  the  putrefaction  of  protein  food  in  the 


370  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVII 

large  intestine.  It  is  absorbed  by  the  blood  and  carried  to  the 
liver,  which  it  is  thought  changes  the  indol  to  indican,  a  less 
poisonous  substance.  Traces  of  indican  are  found  in  normal 
urine,  but  the  presence  of  it  in  any  amount  is  abnormal  and  de- 
notes :  (1)  excessive  putrefaction  of  protein  food  in  the  intestines, 
or  (2)  disease  of  the  stomach.  (1)  Excessive  putrefaction  may  be 
due  to  a  diseased  condition  of  the  intestine  that  interferes  with 
absorption,  to  a  diet  containing  too  much  protein  food,  or  to  con- 
stipation. (2)  In  certain  diseases  of  the  stomach,  food  is  held 
until  it  undergoes  fermentative  changes. 

Acetone.  —  Acetone  is  a  volatile  substance  that  is  thought  to 
be  the  result  of  incomplete  oxidation  of  fats  and  possibly  of  pro- 
teins. It  is  found  in  the  urine  of  individuals  suffering  from  de- 
fective metabolism,  and  in  the  urine  of  normal  individuals  during 
periods  of  fasting. 

Casts.  —  In  some  abnormal  conditions  the  kidney  tubules  be- 
come lined  with  substances  which  harden  and  form  a  mould  or  cast 
inside  the  tube.  Later  these  casts  are  washed  out  by  the  urine, 
and  their  presence  in  urine  can  be  detected  by  the  aid  of  a  micro- 
scope. They  are  named  either  from  the  substances  composing 
them  or  from  their  appearance.  Thus  there  are  (1)  pus  casts, 
(2)  blood  casts,  (3)  epithelial  casts  from  the  walls  of  the  tubes, 
(4)  granular  casts  from  cells  which  have  decomposed  and  form 
masses  of  granules,  (5)  fatty  casts  from  cells  which  have  become 
fatty,  and  (6)  hyaline  casts  which  are  formed  from  coagulable 
elements  of  the  blood. 

Calculi. — Deposits  of  solid  matter  that  have  been  precipitated 
from  the  urine  are  called  urinary  calculi  or  stones.  These  vary  in 
size,  shape,  and  composition ;  the  size  and  shape  being  determined 
largely  by  their  composition  and  location.  They  may  be  formed 
in  any  part  of  the  urinary  tract  from  the  tubules  to  the  external 
orifice  of  the  urethra.  The  causes  which  lead  to  their  formation 
are  (1)  an  increase  in  the  slightly  soluble  constituents  of  the  urine, 
(2)  a  decrease  in  the  amount  of  water  secreted,  and  (3)  abnor- 
mally acid  or  abnormally  alkaline  urine. 

Pus.  —  In  suppurative  conditions  of  any  of  the  urinary  organs 
pus  cells  are  present  in  the  urine. 

Blood.  —  In  cases  of  acute  inflammation  of  any  of  the  urinary 
organs,  of  tuberculosis,  of  cancer,  and  of  renal  stone,  blood  may 


CHAP.  XVII] 


SUMMARY 


371 


be  found  in  the  urine.     If  present  in  large  quantity,  the  urine  is 
deep  red,  and  this  condition  is  known  as  hematuria. 

Toxicity  of  urine.  —  As  urine  is  the  medium  by  which  the  body 
gets,  rid  of  toxic  material,  it  follows  that  urine  itself  is  toxic,  and 
must  be  eliminated,  else  a  condition  of  toxemia  will  result.  This 
condition  is  called  uremia,  because  it  was  thought  that  the  symp- 
toms of  poisoning  were  due  to  the  retention  of  urea  in  the  body. 
It  is  now  believed  that  while  urea  is  poisonous,  it  is  only  one  of 
several  substances  that  renders  urine  toxic.  During  illness  the 
kidneys  always  try  to  eliminate  any  poisonous  substances  that 
find  their  way  into  the  blood,  whether  these  substances  result 
from  defective  metabolism  or  from  bacterial  activity.  This  ac- 
counts for  the  fact  that  after  a  severe  illness  the  kidneys  are  often 
left  in  a  damaged  condition. 

SUMMARY 


Wastes  of 

Cell  Metabolism 


Excretory 
Organs 


Urinary 
System 


Location 


Capsule   and 
supports 


Size 
and 


f  Nitrogenous  salts,  e.g.,  urea. 
]S  (  Inorganic  salts,  e.g.,  sodium  chloride. 

2.  Liquid  —  water. 

3.  Gas  —  carbon  dioxide. 

4.  Solids  — -  waste  materials  from  food. 
Lungs. 

Kidneys. 

Alimentary  Canal. 

Kidneys  (2)  —  secrete  urine. 

Ureters  (2)  —  ducts  which  convey  urine  from  kidneys 

to  bladder. 

Bladder  (1)  —  reservoir  for  urine. 
Urethra  (1)  —  tube  through  which  urine  is  voided. 
Posterior  part  of  lumbar  region,  behind  peritoneum. 
Placed  on  either  side  of  spinal  column  and  extend  from 
upper  border  of  twelfth  thoracic  to  third  lumbar 
vertebra. 

Covered  by  tough  envelope  of  fibrous  tissue. 
Supported  by  pressure  and  counter-pressure  of  neigh- 
boring structures. 
Four  and  one-half  inches  long,  two  and  one-half  inches 

broad,  one  and  one-half  inches  thick. 
Weight,  four  and  one-half  ounces  (130  gms.). 
Bean-shaped,  tubular  glands. 
Concave  side  toward  spine,  convex  side  outward. 
Hilum  —  depression  near  centre  of  concave  side  serves 
for  vessels  to  enter  and  leave. 


372 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVII 


'  Pelvis  —  upper  expanded  end  of  ureter. 

Calyces  —  cup-like  cavities  of  the   pelvis  that   receive 

papillae  of  pyramids. 

Cortex  —  outer,  more  solid  portion. 

Medulla  —  inner,  striated  portion. 

Columns  of  Bertini  —  interpyramidal  extensions  of  corti- 

cal substance. 

Begin  as  hollow  globes  or  capsules  in  the 

Uriniferous 

cortex  of  kidney,  and  after  a  very  ir- 
regular course  open  into  straight  col- 

tubules 

lecting  tubes  which  pour  their  contents 

into  calyces  of  pelvis. 

Cone-shaped  masses  in  the  medullary  por- 

tion of  the  kidney.     Vary  in  number. 

Bases  directed  toward  cortex. 

Pyramids      < 

Papillae  —  apices    of    the    pyramids,    di- 
rected toward  pelvis.  ' 

Consist    of    uriniferous    tubules,    blood- 

vessels, and  lymphatics,  held  together 

[      by  connective  tissue. 

Minute  tufts  of  capillaries  —  glomeruli  — 

Renal 

in  the  cortical  portion  of  kidneys  which 

Anatomy 

corpuscles 

are    surrounded    by    inverted    capsule 

of  the     < 

of  uriniferous  tubule. 

kidney 

Renal  artery  —  direct  from  aorta. 

Enters  hilus  of  kidney,  divides  into  many 

branches. 

Lateral  branches  at  the  level  of 

....        the  base  of  the  pyramids. 

al     1.  Send     branches     to     cortex 

arches             (cortical). 

2.  Send  branches  to  pyramids. 

Blood 

{Lateral  branches  at  level  of  base 

supply 

of  pyramids. 

Receive  blood  from  cortex. 

Receive  blood  from  pyramids. 

Veins  empty  into  renal  vein,  leave  kidney 

at  hilus,  and  empty  into  inferior  vena 

cava. 

Note  —  Blood  from  renal  artery  serves  for 

purposes  of  nourishment  of  kidney  and 

purposes  of  excretion. 

Nerves  from  sympathetic  and  central  ner- 

Nerves   and 

vous  system. 

lymphat- 

Many are  vasomotor,  and  by  regulating  size 

ics 

of  blood-vessels  influence  blood  pressure. 

Well  supplied  with  lymphatics. 

1.  Process  of  mechanical  filtration.    Water 

and  saline  elements  are  filtered  from 

the    blood    during    the    circulation 

through  the  glomeruli. 

Function   < 

Secretion 
of  urine 

2.  Secretory  action  of  the  cells  lining  the 
uriniferous  tubules.    Urea  and  other 

foreign  substances  are  separated  from 

the    blood    during    the    circulation 

through    the    plexus    of    capillaries 

which  surrounds  the  tubules. 

CHAP.  XVII] 


SUMMARY 


373 


Ureters 


Bladder 


Urethra 


Micturition 


Excretory  ducts.  Extend  from  kidneys  to  bladder. 
Consist  of  expanded  portion  called  pelvis  and  duct. 
Size  of  goose-quill.  10-12  in.  long. 

1.  Mucous  —  lining. 

2.  Muscular    1™T>  '""ina!  layer. 


Three 
coats 


Function 


. 

I  Outer,  circular  layer. 
3.  Fibrous  —  carries  blood-vessels  and  nerves. 
(  Connect  kidneys  with  bladder. 
\  Passageway  for  urine. 


Hollow  muscular  organ. 


Situated  in  pelvic  cavity 
behind  the  pubes 


in  front  of  rectum  in  male, 
in   front    of   anterior   wall    of 
vagina  and  neck  of  uterus  in 
female. 

Freely  movable.     Held  in  position  by  ligaments. 
Size,  shape,  and  position  depend  upon  age,  sex,  and  whether 

bladder  is  full  or  empty. 
Fundus  —  widest  part. 

Cervix  —  where  the  bladder  becomes  continuous  with  the 
urethra. 

1 .  Mucous  —  lining. 

2.  Areolar  —  connects  mucous  and  muscular. 

Inner  layer  —  longitudinal. 
Middle  layer  —  circular. 
Outer  layer  —  longitudinal. 
4.  Serous  —  partial    covering    derived    from 

peritoneum. 

Serves  as  a  reservoir  for  the  reception  of  urine. 
When  moderately  distended,  holds  about  one 
pint. 


Four  coats 


Function 


3.  Muscular 


Membranous  canal,  extends  from  the  bladder  to  the  meatus 
urinarius.     1|  in.  long  and  I  in.  in  diameter  in  female. 

Behind  symphysis  pubis,  and  embedded  in  the  anterior 
wall  of  vagina. 

\  1.  Mucous  —  lining. 

Three          !  2.  Submucous  —  supports  network  of  veins, 
coats       |  0  f  Inner  —  longitudinal. 

I  3'Muscular  |  External -circular. 

Meatus  urinarius  —  external  orifice  located  between  cli- 
toris and  vagina. 

Act  of  expelling  urine  from  bladder. 

Occurs  as  result  of  irritation  due  to  accumulation  of  urine 

in  bladder. 
[  Involuntary  act  —  can  be  controlled  by  voluntary  effort. 


374 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XVII 


Due  to 


Failure  to  void  urine. 

1.  Dulling  of  the  senses. 

2.  Nervous  contraction  of  urethra. 
Retention   .    I                       3.  Some  obstruction  in  urethra  or  neck  of 

bladder. 
May  be  accompanied  by  overflow  or  constant  voiding  of 

small  amounts. 
Suppression  —  Failure  of  the  kidneys  to  secrete  urine. 

Transparency  —  depends  on  absence  or  presence  of  mucus 

and  pus. 
Color  —  depends  on  concentration.     Relative  amounts  of 

water  and  solids. ' 
Reaction  —  usually  acid. 

Specific  gravity  —  average  1.020.     Depends  on  concentra- 
tion. 

f     Average  40  to  50  ounces. 

Ingestion    of    large    amount    of 

liquid. 
Urine  .    1  Action  of  diuretics. 

I  nrtraaaari 

Nervousness. 

(  Diabetes  insipidus. 
Diseases  J  Diabetes  mellitus. 

[  Hysteria. 
Ingestion    of    small    amount    of 

liquid. 
Decreased 

by 


Quantity 


Increased 
by 


Vomiting,  diarrhoea. 
High  fever. 
Disease  of  kidneys. 
Increased  action  of  skin. 


Composition , 
of  Urine 


Water, 
95  per  cent 


Soluble 

Salts 

5  per  cent 


Organic 
about  3.7 


Inorganic, 
about  1.3 


f  Urea  (2  per  cent  of  total  solids). 

Uric  acid. 
Purin  bodies      Xanthin. 

Hypoxanthin. 
Creatinin. 
Hippuric  acid. 
Other  substances. 
Sodium  chloride. 
Sulphates. 
Phosphates. 
Potassium. 
Ammonium. 


Magnesium. 

Calcium. 

Other  substances. 


Salts  of 


CHAP.  XVII] 


SUMMARY 


375 


Urea 


Purin 
bodies 

Creatinin 


Hippuric 
acid 


Salts      . 

Abnormal 
constitu- 
ents 


End-product  resulting  from  metabolism  of  proteins. 

Average  excreted  in  twenty-four  hours  —  1  ounce. 

About  0.028  per  cent  present  normally  in  blood  and  tissues. 

Diet  rich  in  proteins. 

Strenuous  exercise  —  hot  baths. 

Some  diseases. 

Small  amount  of  protein  food. 

Excessive  vomiting,  free  perspiration. 

Diseases  that  interfere  with  elimination. 


Increased 
by 


End-products  resulting  from  metabolism  of 
nucleoproteins  of  food  and  tissues. 


Decreased 
by 

Uric  acid 

Xanthin 

Hypoxanthin 

f  It  is  probably  an  end-product  of  the  metabolism  of  protein 
1      tissue. 

Chemical  method  of  defence  against  toxic  substances. 

Digestion  of  fruits  and  vegetables  give  rise  to  toxic  acids, 
e.g.,  benzoic  acid. 

Benzoic  acid  plus  glycocoll  — >•  hippuric  acid. 

Derived  from  food  eaten. 

Derived  from  neutralization  of  acids. 

Sodium  chloride  is  most  abundant. 

Albumin.  Casts. 

Glucose.  Calculi. 

Indican.  Pus. 

Acetone.  Blood. 


CHAPTER  XVIII 

THE  SKIN;  APPENDAGES  OF  THE  SKIN.     BODY  HEAT;  REGULA- 
TION   OF  HEAT.     VARIATIONS   IN   TEMPERATURE 

THE    SKIN 

Functions.  —  The  skin  is  not,  like  the  kidneys,  set  apart  to 
perform  one  special  function.  It  serves  :  (1)  as  a  protective  cov- 
ering for  the  deeper  tissues  lying  beneath  it,  (2)  as  a  sense  organ, 
(3)  as  an  excretory  organ,  (4)  as  an  important  organ  in  heat  regu- 
lation, and  (5)  as  a  respiratory  organ. 

Structure.  —  It  consists  of  two  distinct  layers  :  — 

(1)  Epidermis;  scarf  skin,  or  cuticle. 

(2)  Derma ;  cutis  vera,  or  corium. 

Epidermis.  —  The  epidermis  is  a  stratified  epithelium,  com- 
posed of  a  number  of  layers  of  cells.  It  varies  in  thickness  from 
arc-  inch  (0.104  mm.)  to  ^  inch  (1.04  mm.),  being  thickest 
on  the  palms  of  the  hands  and  on  the  soles  of  the  feet,  where  the 
skin  is  most  exposed  to  friction,  and  thinnest  on  the  ventral  sur- 
face of  the  trunk,  and  the  inner  surfaces  of  the  limbs.  It  forms  a 
protective  covering  over  every  part  of  the  true  skin,  upon  which 
it  is  closely  moulded. 

It  is  roughly  divisible  into  two  layers  :  — 

(1)  Superficial,  or  Horny. 

(2)  Germinative,  or  Malpighian. 

(1)  The  superficial  layer  consists  of  three  strata  of  cells,  which 
are  practically  dead,  and  are  constantly  being  shed  and  renewed 
from  the  cells  of  the  germinative  layer. 

(2)  The  germinative  layer  consists  of  soft  protoplasmic  cells. 
The  growth  of  the  epidermis  takes  place  by  the  multiplication 

of  these  cells.     As  they  multiply  they  push  upward  toward  the 
surface    those    previously    formed.     In    their    upward    progress 

376 


CHAP.  XVIII] 


THE   SKIN 


377 


they  undergo  a  chemical  transformation,  and  the  soft  proto- 
plasmic cells  become  converted  into  the  flat  scales  which  are  con- 
stantly being  rubbed  off  the  surface  of  the  skin.  The  pigment 
in  the  skin  of  the  negro,  as  well  as  that  of  the  nipple  in  white  races, 
is  found  in  the  deepest  cells  of  the  germinative  layer. 


stratum  lucidum 
stratum 
a:?  granulosum 


Gr.  or 


Derma 


FIG.  188.  —  VERTICAL  SECTION  THROUGH  THE  SKIN  OF  THE  PALMAR  SIDE  OF 
THE  FINGER,  SHOWING  Two  PAPILLA  (ONE  OF  WHICH  CONTAINS  A  TACTILE  COR- 
PUSCLE) AND  THE  DEEPER  LAYER  OF  THE  EPIDERMIS.  (Schafer.) 

No  blood-vessels  pass  into  the  epidermis;  it,  however,  receives 
fine  nerve-fibrils  between  the  cells  of  the  germinative  layer. 

Derma.  —  The  derma  is  a  highly  sensitive  and  vascular  layer 
of  connective  tissue.  It  is  described  as  consisting  of  two  layers  :  — 

(1)  Upper,  or  papillary  layer. 

(2)  Deeper,  or  reticular  layer. 

(1)  The  surface  of  the  papillary  layer  is  increased  by  protru- 
sions in  the  form  of  small  conical  elevations,  called  papillae,  whence 
this  layer  derives  its  name.  They  project  up  into  the  epidermis, 


378  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XVIII 

which  is  moulded  over  them,  and  contain  for  the  most  part  looped 
blood-vessels,  but  they  also  contain  the  terminations  of  nerve- 
fibres  in  the  shape  of  little  bodies  called  tactile  corpuscles. 

The  papilla?  seem  to  exist  chiefly  for  the  purpose  of  giving  the 
skin  its  sense  of  touch,  being  always  well  developed  where  the 
sense  of  touch  is  exquisite.  They  are  specially  large  and  numerous 
on  the  palm  of  the  hand  and  the  tips  of  the  fingers,  and  on  the  cor- 
responding parts  of  the  foot. 

(2)  The  reticular  layer  of  the  corium  is  a  continuation  of  the 
papillary  layer,  there  being  no  real  division  between  them.  It  is 
made  up  of  bundles  of  white  fibrous  and  elastic  tissue. 

The  derma  is  attached  to  the  parts  beneath  it  by  a  layer  of 
areolar  tissue,  here  named  subcutaneous,  which  layer,  with  very 
few  exceptions,  contains  fat.  The  connection  in  some  parts  is 
loose  and  movable,  as  on  the  front  of  the  neck;  in  others,  close 
and  firm,  as  on  the  palmar  surface  of  the  hand  and  the  sole  of  the 
foot. 

Blood-vessels.  —  The  blood-vessels  of  the  skin  are  found  in  the 
derma  only.  They  form  a  network  of  capillaries  in  which  the  ves- 
sels are  very  close  to  each  other,  and  send  branches  to  the  papilla? 
and  glands  of  the  skin.  The  capillaries  of  the  skin  are  capable  of 
holding  from  one-half  to  two-thirds  of  the  blood  contained  in  the 
body.  The  amount  of  blood  they  contain  is  dependent  on  their 
caliber,  and  this  is  regulated  largely  by  the  vasomotor  nerves. 

Nerves.  —  The  skin  is  provided  with  a  great  variety  of  nerves.1 
They  are  classified  as  follows  :  — 

(1)  Vasomotor  nerves,  which  are  distributed  in  the  walls  of  the 
blood-vessels. 

(2)  Two  sets  of  nerves  concerned  in  the  temperature  sense, 
which  terminate  in  the  hot  and  cold  spots  of  the  skin. 

(3)  The  nerves  concerned  in  the  sense  of  touch  or  pressure. 

(4)  Nerves  which  are  stimulated  by  pain. 

(5)  Motor  nerves,  which  are  derived  from  the  sympathetic  sys- 
tem and  distributed  to  the  glands  and  the  arrector  muscles. 

Because  of  the  number  of  afferent  nerves  which  lead  from  the 
skin  to  centres  in  the  brain  and  spinal  cord,  nearly  every  nerve 
centre  in  the  body  may  be  affected  by  sensations  arising  in  the  skin. 

1  See  page  430. 


CHAP.  XVIII]  THE  SKIN  379 

It  is  for  this  reason  that  hydro  therapeutic  applications,  heat,  cold, 
and  counter  irritants  excite  so  many  and  such  varied  reflexes. 


THE   APPENDAGES   OF   THE   SKIN 

The  appendages  of  the  skin  are  the  nails,  the  hair,  the  sebaceous 
glands,  the  ceruminous  glands,  and  the  sudoriferous  or  sweat 
glands. 

The  nails.  —  The  nails  are  composed  of  clear,  horny  cells  of 
the  epidermis,  joined  so  as  to  form  a  solid,  continuous   plate. 
Each  nail  is  convex  on  its  outer  surface,  concave   on  its  inner 
side,   and  closely  adherent   to    the   un- 
derlying  derma,    which   is   modified    to 
form  what  is  called  the  bed,  or  matrix, 
of  the  nail.     At  the  hinder  part  of  the          B0ir 
bed  of  the  nail  the  skin  forms  a  deep  fold, 

•  M  LUNULA^ 

in  which  is  lodged  the  root  of  the  nail. 

The  growth  of  the  nail  is  accomplished 
by  constant  multiplication  of  the  soft 
cells  in  the  germinative  layer  at  the  root. 
These  cells  are  transformed  into  dry,  hard 
scales,  which  unite  into  a  solid  plate,  and 

.,  .    .         'IT,.  FIG.  189.  —  THUMB-NAIL. 

the  nail,  constantly  receiving  additions  (Gerrish.) 

from  below,  slides  forward  over  its  bed 

and  projects  beyond  the  end  of  the  finger.  When  a  nail  is  thrown 
off  by  suppuration  or  torn  off  by  violence,  a  new  one  will  grow  in 
its  place  provided  any  of  the  cells  of  the  germinative  layer  are  left. 
The  hair.  —  The  hair  is  a  growth  of  the  epidermis,  developed 
in  little  pits,  the  hair-follicles,  which  extend  downward  into  the 
deeper  part  of  the  true  skin,  or  even  into  the  subcutaneous  tissue. 
The  hair  grows  from  the  bottom  of  the  little  pit  or  follicle.  The 
part  which  lies  within  the  follicle  is  known  as  the  root,  and  that 
portion  which  projects  beyond  the  surface  of  the  skin  is  called  the 
shaft  or  stem.  The  substance  of  the  hair  is  composed  of  coalesced 
horny  cells,  arranged  in  different  layers,  and  we  usually  distinguish 
three  parts  in  the  stem  or  shaft  of  a  hair :  — 

(1)  Cuticle  —  an  outer  layer  of  delicate,  scale-like  cells. 

(2)  Fibrous  substance  —  a  middle  portion,  formed  of  elongated 
cells.    These  cells  and  the  intercellular  spaces  contain  a  varying 


380 


ANATOMY  AND  PHYSIOLOGY    [CHAP.  XVIII 


CUTICLE 


amount  of  pigment,  and  the  color  of  the  hair  depends  upon  the 
quantity.  The  gray  hair  of  old  age  is  produced  by  loss  of  pig- 
ment. 

(3)  Medulla  —  a  central  pith  formed  of  round  cells. 
The  root  of  the  hair  is  enlarged  at  the  bottom  of  the  follicle 
into  a  bulb  or  knob.    This  bulb  is  composed  of  soft-growing 

cells,  and  fits  over  a  vascular  papilla 
which  projects  into  the  bottom  of  the 
follicle.  Hair  has  no  blood-vessels  but 
receives  nourishment  from  the  blood- 
vessels of  the  papilla. 

Growth  of  hair. — Hair  grows  from  the 
bottom  of  the  follicle  by  multiplication 
of  the  soft  cells  which  cover  the  papilla. 
These  cells  become  elongated  to  form 
the  fibres  of  the  fibrous  portion,  and  as 
they  are  pushed  to  the  surface,  they 
become  flattened  and  form  the  cuticle. 
If  the  scalp  is  thick,  pliable,  and  moves 
freely  over  the  skull  it  is  favorable  to 
the  growth  of  hair.  A  thin  scalp  that 
is  drawn  tightly  over  the  skull  tends  to  constrict  the  blood- 
vessels, lessen  the  supply  of  blood,  and  cause  atrophy  of  the 
roots  of  the  hair  by  pressure.  In  such  cases  massage  of  the  head 
loosens  the  scalp,  improves  the  circulation  of  the  blood,  and 
usually  stimulates  the  growth  of  hair. 

With  the  exceptions  of  the  palms  of  the  hands,  the  soles  of  the 
feet,  and  the  last  phalanges  of  the  fingers  and  toes,  the  whole 
skin  is  studded  with  hair.  The  hair  of  the  scalp  is  long  and  coarse, 
but  most  of  the  hair  is  very  fine  and  extends  only  a  little  beyond 
the  hair  follicle. 

Arrector  muscles.  —  The  follicles  containing  the  hairs  are  nar- 
row pits  which  slant  obliquely  upward,  so  that  the  hairs  they  con- 
tain lie  slanting  on  the  surface  of  the  body.  Connected  with  each 
follicle  is  a  small  muscle  called  the  arrector  muscle.  It  is  com- 
posed of  bundles  of  plain  muscular  tissue  which  pass  from  the 
surface  of  the  true  skin,  on  the  side  to  which  the  hair  slopes, 
obliquely  downward,  to  be  attached  to  the  bottom  of  the  follicle. 
When  these  muscles  contract,  as  they  will  under  the  influence  of 


FIBROUS- 
SUBSTANCE 


MEDULLA 

FIG.  190.  —  PIECE  or  HUMAN 
HAIR.     (Highly  magnified.) 


CHAP.  XVIII] 


THE  SKIN 


381 


cold  or  terror,  the  little  hairs  are  pulled  up  straight,  and  stand 
"  on  end  "  ;  the  follicle  also  is  dragged  upward,  and  in  this  way  the 
roughened  condition  of  the  skin  known  as  "  gooseflesh  "  is  pro- 
duced. 

Sebaceous  glands.  —  The  sebaceous  glands  are  small,  saccular 
glands,  which  lie  between  the  hairs  and  their  arrector  muscles. 


SUBCUTANEOUS 
AREOLAR  TISSUE 


.OMERULU8  OF 
SWEAT  GLAND 


BULB  OF  HAIR 
PAPILLA  OFHAI8 


FIG.    191.  —  VERTICAL   SECTION   OP  THE   SKIN,    SHOWING   SEBACEOUS   GLANDS, 
SWEAT-GLANDS,  HAIR  AND  FOLLICLE,  ALSO  ARRECTOR  MUSCLE.     (Gerrish.) 

They  occur  everywhere  over  the  skin  surface,  with  the  exception 
of  the  palms  of  the  hands  and  the  soles  of  the  feet. 

Each  gland  consists  of  a  collection  of  small  tubes  overspread 
with  a  network  of  capillaries.  From  the  gland  a  small  duct  as- 
cends, and  opens  either  upon  the  surface  of  the  skin,  or  as  is  more 
common,  into  a  hair  follicle.  Their  size  is  not  regulated  by  the 
length  of  the  hair.  Thus,  some  of  the  largest  are  found  on  the 
nostrils  and  other  parts  of  the  face,  where  they  often  become  en- 
larged with  pent-up  secretion. 

Sebum.  —  The  secretion  of  the  sebaceous  glands  is  called  sebum. 


382 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVIII 


It  contains  fat,  soaps,  epithelial  cells,  aibuminous  matter,  and 
inorganic  salts.  It  serves  to  remove  waste  matters  and  is  classed 
as  an  excretion,  but  its  more  important  purposes  are  to  keep  the 
skin  and  hair  soft  and  pliable,  and  to  form  a  protective  layer  on 
the  surface  of  the  skin.  An  accumulation  of  this  sebaceous  matter 
upon  the  skin  of  the  foetus  furnishes  the  thick,  cheesy,  oily  sub- 
stance called  the  vernix  caseosa. 

Ceruminous  glands.  —  The  skin  lining  the  external  auditory 
canal  contains  modified  sweat-glands  called  ceruminous  glands. 
They  secrete  a  yellow,  pasty  substance  resembling  wax  which  is 
called  cerumen. 

Sweat-glands.  —  The  sweat-glands  are  simple,  convoluted,  tubu- 
lar glands  with  the  blind  ends  coiled  into  little  balls  which  are 
lodged  in  the  true  skin  or  subcutaneous  tissue ;  from  the  ball  the 

tube  is  continued  as  the  ex- 
cretory duct  of  the  gland 
up  through  the  true  skin 
and  epidermis,  and  finally 
opens  on  the  surface  by 
a  slightly  widened  orifice 
called  a  pore.  Each  tube 
is  lined  by  a  secreting 
epithelium  continuous  with 
the  epidermis.  The  coiled 
end  is  closely  invested  by  a 
mesh  work  of  capillaries,  and 
the  blood  in  the  capillaries 
is  only  separated  from  the 
cavity  of  the  glandular  tube 
by  the  thin  membranes 
which  form  their  respective  walls.  The  secretory  apparatus  in 
the  skin  is  somewhat  similar  to  that  which  obtains  in  the  kid- 
neys; in  the  latter  the  blood-vessels  are  coiled  up  within  the 
tube,  while  in  the  skin  the  tube  is  coiled  up  within  the  mesh- 
work  of  blood-vessels. 

The  sweat-glands  are  abundant  over  the  whole  skin,  but  they 
are  largest  and  most  numerous  in  the  axillae,  the  palms  of  the 
hands,  soles  of  the  feet,  and  the  forehead. 

Perspiration,  or  sweat.  —  The  sweat  is  a  watery,  colorless  liquid, 


FIG.  192.  —  COILED  END  OF  A  SWEAT- 
GLAND,  a,  the  coiled  end  ;  6,  the  duct ;  c,  net- 
work of  capillaries,  inside  which  the  sweat- 
gland  lies. 


CHAP.  XVIII]  THE   SKIN  383 

slightly  turbid,  of  a  salty  taste,  with  a  distinctive  odor  and  an  alka- 
line reaction,  although  when  first  secreted  it  may  be  acid.  It  is 
an  excretion,  the  chief  normal  constituents  of  which  are  water, 
salts,  fatty  acids,  a  small  quantity  of  carbon  dioxide,  and  a  slight 
amount  of  urea.  In  various  forms  of  kidney  disease  urea  may  be 
present  in  considerable  quantity,  the  skin  supplementing  to  a 
certain  extent  the  deficient  work  of  the  kidneys. 

Quantity  of  perspiration  or  sweat.  —  Under  ordinary  circum- 
stances, the  perspiration  that  we  are  continually  throwing  off  evap- 
orates from  the  surface  of  the  booly  without  our  becoming  sensible 
of  it,  and  is  called  insensible  perspiration.  When  more  sweat  is 
poured  upon  the  surface  of  the  body  than  can  be  removed  at  once 
by  evaporation,  it  appears  on  the  skin  in  the  form  of  drops,  and 
we  then  speak  of  it  as  sensible  perspiration. 

The  average  amount  discharged  during  twenty-four  hours  is 
about  one  quart  (1  litre),  but  it  may  be  increased  to  such  an 
extent  that  even  more  may  be  discharged  in  an  hour.  The  secre- 
tion of  sweat  is  increased  by :  (1)  a  dilute  condition  of  the  blood 
such  as  results  from  drinking  large  quantities  of  liquids,  (2)  in- 
creased temperature  or  humidity  of  the  atmosphere,  (3)  exercise, 

(4)  pain,   (5)  mental  excitement  or  nervousness,   (6)   dyspnoea, 
(7)  use  of  diaphoretics,  (8)  certain  diseases,  such  as  tuberculosis, 
acute  rheumatism,  and  malaria,  (9)  use  of  electricity  to  stimulate 
the  secretory  nerves. 

The  secretion  of  sweat  is  decreased  by :  (1)  voiding  of  a  large 
quantity  of  urine,  (2)  cold,  (3)  diarrhoea,  (4)  certain  drugs,  and 

(5)  certain  diseases,  such  as  fevers,  diabetes,  and  some  cases  of 
paralysis. 

Activity  of  the  sweat-glands.  —  Experimental  work  with  animals 
has  led  some  observers  to  believe  (1)  that  there  is  a  definite  sweat 
centre  in  the  brain.  The  exact  location  of  this  centre  has  not  been 
determined,  but  reasoning  from  analogy  it  seems  probable  that  it 
may  be  located  in  the  medulla.  (2)  That  definite  secretory  nerves 
from  this  centre  are  distributed  to  the  sweat-glands. 

The  activity  of  these  glands  may  be  influenced  by  external 
heat,  dyspnoea,  muscular  exercise,  and  the  action  of  various  drugs. 
In  all  such  cases  the  effect  is  supposed  to  be  the  result  of  either 
direct  stimulation  of  the  nerve-endings  in  the  glands,  or  indirect 
stimulation  through  the  nerve  centres.  The  common  cause  of 


384  ANATOMY  AND  PHYSIOLOGY    [CHAP.  XVIII 

profuse  sweating  is  a  high  external  temperature  or  muscular  ex- 
ercise. It  is  known  that  the  high  temperature  acts  upon  the  sen- 
sory cutaneous  nerves  and  stimulates  the  sweat  fibres  indirectly 
through  the  nerve  centres,  and  possibly  directly  by  increasing  the 
irritability  of  the  nerve-endings. 

Excretory  function  of  the  skin.  —  While  sweat  is  an  excretion, 
its  value  lies  not  so  much  in  the  elimination  of  waste  matter  as  in 
the  loss  of  body  heat  by  the  evaporation  of  water.  Each  gram  of 
water  requires  about  0.5  calorie  to  cause  it  to  evaporate,  and  this 
heat  is  taken  from  the  body.  This  loss  of  heat  helps  to  balance 
the  production  of  heat  that  is  constantly  taking  place. 

BODY   HEAT 

From  the  standpoint  of  heat  production  animals. may  be  divided 
into  two  great  classes  :  — 

(1)  Constant  temperature 1  animals,  or  those  whose  temperature 
remains  practically  constant  whether  the  surrounding  air  is  hotter 
or  cooler  than  the  body.     The  term  warm-blooded  is  also  applied 
to  this  class.     It  includes  human  beings. 

(2)  Variable  temperature  2  animals,  or  those  whose  tempera- 
ture varies  with  that  of  the  surrounding  medium.     This  class  is 
also  described  as  cold-blooded.     The  human  foetus  is  cold-blooded. 

The  great  difference  between  these  two  classes  is  in  their  reac- 
tions to  external  temperature.  A  cold  environment  reduces  the 
temperature  of  the  cold-blooded  creature,  reduces  the  metabolism 
of  all  its  tissues,  and  thus  reduces  its  heat  production.  The 
warm-blooded  animal  reacts  in  precisely  the  opposite  way.  Since 
his  temperature  remains  constant,  his  heat  production  must  in- 
crease in  order  to  neutralize  the  effect  of  cold  surroundings. 

Production  of  heat.  —  Heat  in  the  body  is  produced  by  such 
chemical  changes  going  on  in  the  tissues  as  are  associated  with 
oxidation.  Friction  is  a  minor  source  of  heat,  i.e.,  that  caused  by 
the  movements  of  the  muscles,  the  circulation  of  the  blood,  and 
the  ingestion  of  warm  food. 

Where  heat  is  produced.  —  Wherever  metabolic  changes  are  tak- 
ing place,  there  heat  is  set  free.  These  changes  take  place  more 
rapidly  in  some  tissues  than  in  others,  and  in  the  same  tissues 

1  Homothermous,  2  Poikilothermous. 


CHAP.  XVIII]  BODY   HEAT  385 

at  different  times.  The  muscles  always  manifest  a  far  higher  rate 
of  activity  than  the  connective  tissues,  and  consequently  the 
former  evolve  a  larger  proportion  of  the  bodily  heat  than  the  latter. 
We  might  liken  the  different  tissues  of  the  body  to  so  many  fire- 
places stored  with  fuel,  the  fuel  in  some  of  the  fireplaces  being  more 
easily  ignited  and  burning  more  rapidly  than  in  others.  The 
muscles  and  the  secreting  glands,  especially  the  liver,  are  sup- 
posed to  be  the  main  sources  of  heat,  as  they  are  the  seats  of  a  very 
active  metabolism. 

Loss  of  heat.  —  The  heat  thus  continually  produced  is  as  con- 
tinually leaving  the  body  by  the  skin  and  the  lungs,  and  by  the 
urine  and  feces  which  are  at  the  temperature  of  the  body  when 
voided.  It  has  been  calculated  that  in  every  100  parts,  about :  — 

73.0  per  cent  is  lost  by  conduction  and  radiation. 
14.5  per  cent  is  lost  by  evaporation. 
10.7  per  cent  is  lost  by  expired  air :  — 

(a)  vaporization  of  water,  7.2  per  cent. 

(6)  warming  of  air,  3.5  per  cent. 
1.8  per  cent  is  lost  by  urine  and  feces. 

The  temperature  and  humidity  of  the  atmosphere  may  cause 
considerable  difference  in  the  per  cents  given  above.  A  low  tem- 
perature will  increase  the  loss  of  heat  by  radiation  and  decrease 
that  by  evaporation.  A  high  temperature  will  decrease  the  loss 
of  heat  by  radiation  and  increase  that  by  evaporation,  owing  to 
the  greater  production  of  sweat.  From  the  above  figures  it  is 
evident  that  the  skin  is  the  important  factor  in  getting  rid  of  body 
heat.  This  is  due :  (1)  to  the  large  surface  offered  for  radiation, 
conduction,  and  evaporation;  and  (2)  to  the  large  amount  of 
blood  which  it  contains. 

Distribution  of  heat.  —  The  blood,  as  we  know,  permeates  all 
the  tissues  in  a  system  of  tubes  or  blood-vessels.  Wherever 
oxidation  takes  place  and  heat  is  generated,  the  temperature  of 
the  blood  circulating  in  these  tissues  is  raised.  Wherever,  on 
the  other  hand,  the  blood-vessels  are  exposed  to  evaporation,  as 
in  the  moist  membranes  in  the  lungs,  or  the  more  or  less  moist 
skin,  the  temperature  of  the  blood  is  lowered.  The  gain  and 
loss  of  heat  balance  one  another  with  great  nicety,  and  the  blood, 
circulating  rapidly,  now  through  warmer,  and  again  through  cooler, 
tubes,  is  kept  at  a  uniform  temperature  of  about  100°F.  (37.8°C.). 
2c 


386  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVIII 

In  this  way  the  whole  body  is  warmed  in  somewhat  the  same 
way  as  we  warm  a  house,  the  warm  blood  in  the  blood-vessels 
heating  the  tissues,  as  the  hot  water  in  the  hot-water  pipes  heats 
the  rooms  in  water-heated  dwellings. 

THE  REGULATION  OF  BODY  HEAT 

The  regulation  of  body  heat  is  due  to  the  maintenance  of  a 
certain  balance  between  heat  production  and  heat  dissipation. 
To  many  physiologists  it  has  seemed  reasonable  to  suppose  that  this 
balance  was  controlled  by  a  definite  set  of  heat  nerves  connected 
with  heat  centres  in  the  brain.  While  such  an  apparatus  may  exist 
the  evidence  in  favor  of  it  is  not  convincing,  and  the  conservative 
view  is  that  the  control  of  heat  production  and  heat  dissipation  is 
effected  by  the  coordinated  activities  of  different  centres  plus 
such  voluntary  means  as  (1)  the  regulation  of  muscular  exercise 
and  diet,  (2)  the  use  of  suitable  clothing,  and  (3)  the  use  of  hot  and 
cold  baths. 

The  involuntary  regulation  of  the  body  temperature  is  effected 
chiefly  through  the  following  centres :  — 

1.  The  quantity  and  character  of  food. 

2.  The  motor  nerve  centres  and  the  motor  fibres  to  the 

skeletal  muscles. 
1.  The  respiratory  centre. 

Heat  2.  The  sweat  centres  and  sweat  nerves. 

Dissipation    3.  The  vaso-constrictor  centres  and  nerves  distributed  to  the 

skin. 

Heat  production.  —  (1)  In  a  previous  chapter  we  described  how 
the  oxidation  of  different  foodstuffs  produced  varying  amounts  of 
heat.  (2)  The  motor  nerve-fibres  which  are  distributed  to  the 
skeletal  muscles  are  indirectly  stimulated  by  cold.  It  causes  the 
muscles  to  contract  and  speeds  up  the  processes  of  oxidation. 

Heat  dissipation.  —  (1)  The  stimulation  of  the  sensory  nerves 
of  the  skin  that  are  affected  by  cold  influences  the  respiratory  cen- 
tre, increases  the  rate  of  the  respirations,  and  consequently  in- 
'  creases  the  loss  of  heat.  In  man  respiration  plays  only  a  small 
part  in  heat  regulation,  but  in  animals  that  do  not  perspire,  res- 
piration is  an  important  means  of  regulating  the  temperature. 

(2)  When  the  external  temperature  is  high,  the  nerve-endings 
which  respond  to  heat  are  stimulated,  and  these  impulses  are 


CHAP.  XVIII]  BODY  HEAT  387 

transmitted  over  sensory  nerves  to  the  nerve  centres  controlling 
the  motor  nerves  of  the  sweat-glands.  The  motor  nerves  stimu- 
late the  activity  of  the  sweat-glands,  and  an  increased  amount  of 
sweat  is  poured  out  upon  the  surface  of  the  body.  An  increased 
amount  of  heat  is  required  to  vaporize  this  sweat,  and  thus  heat  is 
lost.  Excessive  humidity  interferes  with  the  evaporation  of 
water,  and  thus  interferes  with  the  loss  of  heat;  hence  the  dis- 
comfort experienced  on  hot,  humid  days. 

(3)  The  sensory  nerves  which  are  stimulated  by  heat  not  only 
transmit  impulses  that  stimulate  the  sweat-glands  to  activity,  but 
at  the  same  time  transmit  impulses  that  result  in  the  depression 
of  the  vaso-constrictor  nerves  of  the  arterioles  of  the  skin.  In  con- 
sequence the  arterioles  dilate  and  more  blood  is  sent  to  the  surface 
to  be  cooled.  When  the  external  temperature  is  low,  the  sensory 
nerve-endings  which  are  stimulated  by  cold  transmit  impulses 
which  result  in  stimulation  of  the  vaso-constrictors,  and  conse- 
quent contraction  of  the  arterioles  of  the  skin.  This  lessens  the 
amount  of  blood  in  the  skin  arterioles,  and  lessens  the  amount 
of  heat  lost. 

The  voluntary  regulation  of  body  temperature  is  effected  by 
the  following  means  :  — 

By  muscular  exercise  and  diet.  —  Muscular  contractions  give 
rise  to  heat,  therefore  muscular  activity  is  used  as  a  means  to 
counteract  the  effects  of  external  cold.  On  the  other  hand, 
muscular  activity  does  not  increase  the  temperature  in  hot  weather 
to  any  marked  extent.  This  is  accounted  for  by  the  fact  that  when 
muscular  exertion  causes  the  blood  to  circulate  more  quickly  than 
usual,  the  blood-vessels  in  the  skin  dilate,  the  sweat-glands  at  the 
same  time  are  excited  to  pour  out  a  more  abundant  secretion, 
and  the  heated  blood  passing  in  larger  quantities  through  the  cu- 
taneous vessels  (which  are  kept  well  cooled  by  the  evaporation  of 
the  perspiration),  the  general  average  temperature  of  the  body  is 
maintained. 

During  digestion  heat  is  produced  partly  by  the  peristaltic  ac- 
tion of  the  intestines,  and  partly  by  the  activity  of  the  various 
digestive  glands  (particularly  the  liver).  The  quantity  of  food 
eaten,  and  the  relative  amount  of  heat-producing  food,  influence 
the  temperature  of  the  body.  In  cold  weather  an  increase  in  food 
(usually  accompanied  by  an  increase  of  fats)  serves  to  replace  the 


388  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XVIII 

greater  amount  of  heat  lost.  When  muscular  exercise  is  impos- 
sible, as  in  infants,  an  increase  in  fats  serves  the  same  purpose  as 
exercise  in  a  healthy  adult. 

By  clothing.  —  By  clothing  we  can  aid  the  functions  of  the  skin 
and  the  maintenance  of  heat ;  though,  of  course,  clothes  are  not 
in  themselves  sources  of  heat.  Clothing  of  any  kind  captures  a 
layer  of  warm  and  moist  air  between  it  and  the  skin,  and  thus 
diminishes  greatly  the  loss  by  evaporation  and  radiation.  In 
considering  the  heat  value  of  clothing  the  important  properties 
are :  (1)  whether  it  is  loosely  or  tightly  woven,  (2)  its  thickness, 
and  (3)  its  color. 

(1)  Materials  that  are  loosely  woven  will  be  warmer  than  those 
that  are  tightly  woven,  because  the  meshes  in  a  loosely  woven 
material  are  capable  of  holding  air,  which  is  a  poor  conductor 
of  heat,  and  thus  prevents  radiation. 

(2)  Thick  material  does  not  allow  cold  air  to  penetrate  to  the 
skin. 

(3)  Dark-colored  materials  absorb  heat  to  some  extent,  hence 
they  are  warmer  than  light-colored  textiles.     Thick,  porous  ma- 
terials are  used  to  keep  the  body  warm.     Wool  has  an  additional 
advantage,  as  evaporation  takes  place  more  slowly  from  it  than 
from  linen,  cotton,  or  silk.     Thin  and  very  porous  materials  help 
to  keep  the  body  cool,  because  they  allow  the  air  to  penetrate  to 
the  skin,  and  thus  assist  the  evaporation  of  sweat. 

Hot  baths.  —  The  primary  effect  of  a  hot  bath  is  to  prevent 
radiation  of  heat  from  the  surface  of  the  body,  and  some  increase 
in  temperature  may  result.  If  the  bath  is  not  continued  for  too 
long  a  time,  this  effect  is  counteracted  by  the  increased  perspira- 
tion that  follows. 

Cold  baths.  —  The  primary  effect  of  a  cold  bath  is  similar  to  the 
effect  of  cold  air.  The  cold  contracts  the  arterioles  of  the  skin, 
drives  the  blood  to  the  interior,  and  increases  oxidation.  If  the 
bath  is  a  short  one  and  is  followed  by  friction,  the  reaction  is  for 
the  arterioles  to  dilate,  the  heated  blood  is  sent  to  the  surface,  the 
circulation  is  quickened,  and  there  is  a  consequent  loss  of  heat. 
In  health  the  gain  in  heat  is  usually  balanced  by  the  loss  of  heat, 
and  the  purpose  of  a  cold  bath  is  to  exercise  the  arterioles  and 
stimulate  the  circulation.  If  the  bath  is  continued  for  some  time, 
the  temperature  of  the  skin,  and  of  the  muscles  lying  beneath,  is 


CHAP.  XVIII]  TEMPERATURE  389 

reduced,  and  either  the  heat-producing  processes  may  be  checked 
and  a  loss  of  temperature  result ;  or  shivering  may  intervene.  In 
this  case  the  muscular  contractions  and  constriction  of  the  blood- 
vessels stimulate  metabolism  and  heat  production.  When  cold 
baths  are  given  for  the  purpose  of  increasing  heat  elimination, 
friction  is  used  during  the  bath  to  prevent  shivering.  Friction 
stimulates  the  sensory  nerves  of  the  skin,  causes  dilatation  of  the 
arterioles,  and  favors  the  flow  of  hot  blood  to  the  surface,  thus 
decreasing  the  sensation  of  cold  and  increasing  heat  elimination. 
If  properly  given,  cold  baths  stimulate  the  nervous  system,  im- 
prove the  tone  of  the  muscles,  including  the  muscles  of  the  heart 
and  blood-vessels,  stimulate  the  circulation,  and  favor  the  elimi- 
nation of  heat. 

VARIATIONS  IN  TEMPERATURE 

Normal  variations.  —  The  temperature  of  the  human  body  is 
usually  measured  by  thermometers  placed  in  the  mouth,  axilla, 
or  rectum.  Such  measurements  show  slight  variations,  as  the 
temperature  in  the  interior  of  the  body  is  slightly  higher  than  on 
the  surface  of  the  skin.  The  average  temperature  in  the  rectum  1 
is  98.9°  F.,  in  the  axilla  is  98°  F.,  in  the  mouth  is  98.3°  F. 

Other  normal  variations  depend  upon  the  manner  of  living, 
time  of  eating,  age,  etc.  The  lowest  temperature  is  usually  in  the 
early  morning,  it  rises  slowly  during  the  day,  reaches  its  maximum 
in  the  evening,  and  falls  again  during  the  night.  This  corresponds 
to  the  usual  temperature  ranges  in  fever,  when  the  minimum  is 
in  the  early  morning,  and  the  maximum  is  in  the  evening.  Mus- 
cular activity  and  food  may  cause  a  slight  increase  in  tempera- 
ture during  the  day.  Age  has  some  influence.  Infants  and  young 
children  have  a  slightly  higher  temperature  than  adults.  It  is 
also  true  that  the  heat-regulating  mechanism  in  infants  2  and  young 
children  is  not  so  efficient  as  in  adults,  consequently  they  are  more 
subject  to  changes  of  body  temperature,  and  these  changes  are  not 
as  significant  as  they  would  be  with  adults.  Aged  people  show  a 

1  Rectal  temperature  is  the  most  reliable  ;  and  that  by  mouth  (if  properly  taken) 
is  almost  equally  reliable.     Axillary  temperature  has  little  value. 

2  At  birth  the  heat-regulating  mechanism  is  not  "  in  working  order,"  and  during 
the  first  few  weeks  of  life  infants  are  not  able  to  regulate  their  body  temperature, 
hence  the  importance  of  keeping  them  warm.     Premature  infants  are  even  less  able 
to  regulate  their  body  temperature,  hence  need  of  special  means  to  keep  them  warm. 


390  ANATOMY  AND   PHYSIOLOGY   [CHAP.  XVIII 

tendency  to  revert  to  infantile  conditions,  and  their  temperature 
is  usually  slightly  higher  than  in  middle  life. 

Abnormal  variations.  Fever.  —  The  term  fever  is  applied  to 
an  abnormal  condition,  characterized  by  increased  temperature, 
increased  heart-beat,  increased  respiration,  increased  tissue  waste, 
and  faulty  secretion. 

Cause.  —  The  exact  cause  of  fever  is  unknown.  It  is  the  result 
of  causes  which  disturb  the  balance  between  heat  production  and 
heat  elimination.  One  theory  is  that  toxic  substances  circulating 
in  the  blood  or  abnormal  conditions  of  the  various  organs  of  the 
body  may  interfere  with  the  proper  functioning  of  various  nerve 
centres.  The  toxic  substances  circulating  in  the  blood  may  result 
from  faulty  metabolism,  as  in  diabetes,  gout,  etc. ;  or  from  the 
action  of  bacteria,  as  in  infectious  diseases ;  or  from  injury  to  the 
tissues  of  a  mechanical,  thermal,  or  chemical  nature. 

Value  of  fever.  —  When  fever  is  due  to  infection  by  bacteria, 
the  body  seems  better  able  to  fight  the  infection  if  the  tempera- 
ture is  elevated.  For  this  reason  fever  is  thought  to  be  a  protec- 
tive measure  and  antipyretics  are  not  used  unless  the  elevation  is 
extreme,  or  long  continued.  In  such  cases  measures  must  be 
taken  to  reduce  the  temperature,  or  death  may  ensue  from  coagu- 
lation of  the  body  proteins. 

Subnormal  temperature.  —  In  some  maladies  the  temperature 
falls  distinctly  below  normal.  This  is  due  chiefly  to  dimin- 
ished metabolism.  In  cases  of  starvation  the  fall  of  tem- 
perature is  very  marked,  especially  during  the  last  days  of  life. 
The  diminished  activity  of  the  tissues  first  affects  the  central 
nervous  system ;  the  patient  becomes  languid  and  drowsy,  and 
finally  unconscious;  the  heart  beats  more  and  more  feebly,  the 
breath  comes  more  and  more  slowly,  and  the  sleep  of  unconscious- 
ness passes  insensibly  into  the  sleep  of  death. 


CHAP.  XVIII] 


SUMMARY 


391 


Skin 


Func- 
tions 


Con- 
sists of 


SUMMARY 

1.  Protective  covering  for  deeper  tissues. 

2.  As  a  sense  organ. 

3.  As  an  excretory  organ. 

4.  Most  important  as  organ  in  heat  regulation. 

Small  amount  oxygen  taken  in. 
Small  amount  carbon  dioxide 
is  thrown  off. 


5.  As  a  respiratory  organ 


Derma    is 

a     layer 
of    con- 
nective 
tissue 


Superfi- 
cial   or 
horny 


b. 


a.  Stratum 

corneum 
Stratum 

lucidum 
Stratum 

granulo- 

sum 


Practically 
dead  cells 
being  con- 
stantly shed 
and  renewed 
from  germi- 
native  layer. 


Soft  protoplasmic  cells  that 
are  constantly  multiplying 
by  cell  division. 


Epidermis 
is  a  strat- 
ified epi- 
thelium 

2.   Germina- 

tive  or 

Mal- 

pighian 

1 .  Papillary  layer  —  papillae  are  minute  coni- 

cal elevations  of  the  cutis  vera.  They 
contain  looped  blood-vessels  and  ter- 
minations of  nerve-fibres  called  tactile 
corpuscles. 

Bundles  of  fibrous  and  elastic 

2.  Reticular        tissue,     with    network    of 

layer  blood-vessels,     lymphatics, 

and  nerves. 

Blood-vessels  —  They  are  found  in  derma  only.  Send  branches 
to  papilla?  and  glands  of  skin.  Capable  of  holding  one-half  to 
two-thirds  total  amount  of  blood  in  body. 


Nerves 


Appendages 


Vasomotor. 

Two  sets  concerned  in  temperature  sense. 

Nerves  concerned  in  sense  of  touch  or  pressure. 

Nerves  stimulated  by  pain. 

Motor  nerves  from  sympathetic  system. 

Nails. 

Hair.       ' 

Sebaceous  glands. 

Ceruminous  glands. 

Sweat-glands. 


392 


ANATOMY  AND   PHYSIOLOGY    -[CHAP.  XVIII 


Nails 


Hair 


Sebaceous 
Glands 


Ceruminous 
Glands 


Sweat- 
glands 


Sweat 


Consist  of  clear,  horny  cells  of  epidermis. 
.  True  skin  forms  a  bed  or  matrix  for  nail. 
|  Root  of  nail  is  lodged  in  a  deep  fold  of  the  skin. 
[  Nails  grow  from  soft  cells  in  germinative  layer  at  root. 

The  hair  grows  from  the  roots. 

The  roots  are  bulbs  of  soft,  growing  cells  contained  in  the 
hair  follicles. 

Hair  follicles  are  little  pits  developed  in  the  derma. 

Stems  of  hair  extend  beyond  the  surface  of  the  skin,  con- 
sist of  three  layers  of  cells :  (1)  cuticle,  (2)  fibrous 
substance,  and  (3)  medulla. 

{  Palms  of  the  hands. 
Found  all  over  I  „  .       f   ,     , 
,     ,  Soles  of  the  feet. 

[  Last  phalanges  of  the  fingers  and  toes. 

Arrector  muscles  are  attached  to  true  skin  and  to  each  hair 
follicle. 

Saccular  glands  the  ducts  of  which  usually  open  into  a 
hair  follicle,  but  may  discharge  separately  on  the  sur- 
face of  the  skin. 

Lie  between  arrector  muscles  and  hairs. 

,  [  Palms  of  hands. 
1  ound  over  entire  skin  surface  except  i  0  • .       r  ,. 

I  Soles  of  feet. 

Secrete  sebum,  a  fatty,  oily  substance,  which  keeps  the 
hair  glossy,  the  skin  flexible,  and  forms  a  protective 
layer  on  surface  of  skin. 

Modified  sweat-glands. 

Found  in  skin  of  external  auditory  canal. 

Secrete  cerumen,  a  yellow,  pasty  substance,  like  wax. 

Tubular  glands,  consist  of  blind  ends  coiled  in  balls, 
lodged  in  subcutaneous  tissue,  and  surrounded  by  a 
capillary  plexus.  Secrete  sweat  and  discharge  it  by 
means  of  ducts  which  open  exteriorly.  (Pores.) 

Watery,  colorless,  turbid  liquid,  salty  taste,  distinctive 
odor,  and  an  alkaline  reaction. 

Consists  of  water,  salts,  fatty  acids,  urea,  and  carbon 
dioxide. 

Average  quantity,  one  quart  in  twenty-four  hours. 

1.  Dilute  condition  of  blood. 

2.  Increased  temperature  or  humidity 

of  the  atmosphere. 
Amount  increased  I  3.  Exercise, 
by  4.  Pain. 

5.  Mental  excitement  or  nervousness. 

6.  Dyspnoea. 

7.  Use  of  diaphoretics. 


CHAP.  XVIII] 


SUMMARY 


393 


Sweat 


Activity  of 
Sweat- 
glands 

Excretory 
Function 


Body  Heat 


Amount  increased 
by 


8.  Certain  diseases 


Tuberculosis. 
Acute     rheuma- 
tism. 
Malaria. 

9.  Use    of    electricity    to    stimulate 
secretory  nerves. 

1.  Voiding  a  large  quantity  of  urine. 

2.  Cold. 

3.  Diarrhoea. 

4.  Certain  drugs. 

Fevers. 


5.  Certain  diseases 


Animals  divided 
into  2  classes 


Amount  decreased 

by 

Diabetes. 
Some  paralyses. 
Controlled  by  definite  secretory  nerves  leading  to  centre 
in  brain. 

1 .  Direct  stimulation  of  nerve-ending  in  sweat-glands. 

2.  Indirect  stimulation  of  nerve  centres. 

Importance  not  in  elimination  of  waste  substances  in 
perspiration,  but  because  of  heat  needed  to  cause  evap- 
oration of  perspiration. 

1.  Homothermous     or     those     which 

have  an  almost  constant  tempera- 
ture. 
Human  beings  are  in  this  class. 

2.  Poikilothermous     or     those     whose 

temperature    varies    with  that  of 
their  environment. 
The  human  fcetus  is  cold-blooded. 
Chemical    changes    associated    with 

oxidation. 

Friction  of  muscles,  blood,  etc. 
Ingestion  of  warm  food. 
Wherever    metabolic  .  changes     are 
taking  place. 

Offers    large     surface    for 
radiation,       conduction, 
and  evaporation  of  sweat. 
Contains  large  amount  of 

blood. 

Lungs  —  10.7  per  cent  is  lost  warming 
the  expired  air  and  the  evaporation 
of  the  water  of  respiration. 
Urine  and  Feces  —  1.8  per  cent  is  lost 

warming  the  urine  and  feces. 
Distributed  —  by    the    blood    circulating    through    the. 
blood-vessels. 


Produced  by 


Lost  by 


Skin  87.5 
per  cent 


394 


ANATOMY  AND  PHYSIOLOGY    [CHAP.  XVIII 


Due  to  maintenance  of  balance  between  heat  production 

and  heat  dissipation. 

Heat 

1.  The  quantity  and  character  of  food. 

Production 

2.  The  motor  nerve  centres  and  the 
motor  fibres  to  the  skeletal  muscles. 

1.  The  respiratory  centre. 

Heat 

2.  The  sweat  centres  and  sweat  nerves. 

Dissipation 

3.  The    vaso-constrictor    centres    and 

Regulation 

nerves  distributed  to  the  skin. 

of  Body  Heat 

1.  The  coordinated  activities  of  all  the 

different  nerve  centres. 

(a)  Regulation  of  mus- 

cular exercise  and 

Controlled  by 

diet. 

2.  Voluntary  4 

(6)  Use      of      suitable 

means 

clothing. 

| 

(c)  Use  of  hot  and  cold 

baths. 

Variations  in 
Temperature 


Normal 


1.  Depends  on  where  temperature  is 
taken 


Abnormal 


Mouth. 

Axilla. 

Rectum. 

2.  Depends  on  time  j  Lowest  in  early  morning. 

of  day  1  Highest  in  early  evening. 

3.  Slightly  increased  by  muscular  activity  and 

the  digestive  processes. 

4.  Age.     Higher  and  f  Infants,  children,  and 

more  variable  in  I      the  aged. 

Increased  temperature. 
Increased  pulse. 
Increased  respiration. 
Increased  tissue  waste. 
Faulty  secretion. 
Cause  —  not  definitely  known. 
Value  —  thought  to  help  the  body  to 
I      fight  infection. 
Subnormal  —  due  to  diminished  metabolism. 


Fever 


Symptoms 


CHAPTER  XIX 


A.P. 


THE   NERVOUS   SYSTEM 

As  brought  out  in  Chapter  III  in  the  section  on  nerve  tissue, 
the  structural  and  functional  unit  of  the  nervous  system  is  the 
neurone.  Neurones  as  there  described  are  large  irregular  cells 
with  elongated  processes,  one  of  which  is 
an  axone,  and  one  or  more  of  which  are 
dendrites.  (See  Figs.  16  and  18.) 

The  reflex  concept.  —  In  the  same  way 
that  the  nervous  system  may  be  reduced 
to  a  simple  unit  designated  as  the  neurone, 
so  may  all  nervous  action  be  reduced  to 
the  so-called  reflex  action.  Just  as  the 
neurone  forms  the  building  stone  of  the 
nervous  system,  so  does  the  reflex  circuit 
form  the  functional  basis  of  all  nervous 
activity.  At  least  two  neurones  enter 
into  the  formation  of  a  reflex  circuit,  a 
receptor  or  sensory  neurone  and  an  effector 
or  motor  neurone. 

A  receptor  or  sensory  neurone  is  one  in 
which  the  afferent  process  ends  in  a  re- 
ceptor of  one  kind  or  another.  .  An  effector 
or  motor  neurone  is  one  in  which  the  effer- 
ent process  ends  in  a  muscle  or  gland  cell. 
Neurones  wrhich  are  interpolated  between 
other  neurones  are  called  central  or  cor- 
relation neurones. 

A  simple  reflex  circuit  may  consist  in 
the  functioning  of  a  sensory  and  a  motor  neurone.  Most  reflex 
circuits  consist  in  the  functioning  of  a  sensory  neurone,  a  corre- 
lation or  central  neurone,  and  a  motor  neurone,  or.  by  complexes 
of  each  of  these. 

395 


FIG.  193.  —  A  REFLEX 
CIRCUIT  CONSISTING  OF  A 
SENSORY  AND  MOTOR 
NEURONE.  R,  receptor ; 
A.  P.,  afferent  process; 
S,  synapse ;  E.  P.,  efferent 
process ;  E,  effector  (mus- 
cle). (Burton-Opitz.) 


396  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XIX 

Synapse.  —  We  conceive  each  neurone  to  be  a  separate  entity 
and  not  directly  connected  with  other  neurones.  The  fine  branches 
of  an  axone  of  one  neurone  interlace  or  dovetail  with  the  branches 
of  a  dendrite  of  another  neurone,  forming  a  synapse.  The  nerve- 
impulse  travelling  through  a  nerve-cell  must  cross  a  microscopic 
gap  at  the  synapse  to  enter  the  next  neurone. 

Figure  193  illustrates  a  reflex  circuit  consisting  of  a  sensory  and  a 
motor  neurone.  Figure  194  illustrates  a  reflex  circuit  consisting  of 
a  sensory,  cbrrelation,  and  motor  neurone. 


M 


FIG.   194.  —  A  REFLEX  CIRCUIT  CONSISTING  OF  A  SENSORY,  CORRELATION, -AND 
MOTOR  NEURONE.     S,  sensory  cell ;  C,  central  or  correlation  cell ;  M,  motor  cell. 

On  applying  an  appropriate  stimulus  to  the  receptor  ending  of 
the  sensory  neurone,  an  impulse  is  generated  which  passes  along 
the  afferent  process  to  the  cell-body  of  the  neurone,  thence  along 
the  efferent  process  across  the  synapse  through  the  correlation 
neurone  and  across  another  synapse  to  an  afferent  process  of  the 
motor  neurone,  then  through  the  cell-body  and  an  efferent  process 
to  the  muscle  or  gland  cell  where  action  is  produced.  (Trace  this 
out  in  Fig.  194.) 

Because  of  its  likeness  to  a  telephone  system  the  peripheral  end 
of  the  sensory  nerve  is  often  called  the  receptor  (telephone  trans- 
mitter). The  processes  are  called  carriers  (telephone  wires),  the 
synapses  and  cell-bodies  are  called  adjusters  (telephone  operators), 
and  the  ending  in  muscle  or  gland  cell  an  effector  (telephone  re- 
ceiver). The  receptor  receives  the  stimulus,  transforms  it  to  a 
nerve-impulse,  and  passes  it  on  to  the  afferent  process.  In  the 
adjusting  mechanism  the  nerve-impulse  may  be  transferred  across 
some  synapses  rather  than  others  for  it  must  be  remembered  that 
each  neurone  forms  synapses  not  simply  with  one  neurone,  as  in 
Fig.  194,  but  probably  with  many,  as  in  Fig.  195. 


CHAP.  XIX]          THE  NERVOUS  SYSTEM 


397 


Reaction  circuit.  —  When  cells  in  the  volitional  centres  enter 
into  the  reflex  circuit  the  resulting  action  is  due  to  volition  or  is 
voluntary,  as  we  say.  This  reflex  circuit  is  called  a  reaction  cir- 
cuit. In  Fig.  195  the  circuit  starting  at  R  and  running  through 


CEREBELLUM 


WHITE  MATTER 
OF  SPINAL  CORD 


FIG.  195.  —  DIAGRAM  TO  ILLUSTRATE  SOME  REFLEX  CIRCUITS  OF  THE  CEREBRO- 
SPINAL  SYSTEM,  SHOWING  A  NUMBER  OF  CORRELATION  AND  MOTOR  CELLS  WITH 
THEIR  SYNAPSES.  1,  sensory  cell  in  spinal  ganglion;  2,  2',  2",  2'",  motor  cells; 
3,  3',  3",  4,5,6,  7,  correlation  cells,  a,  afferent  process ;  e,  efferent  process ; 
s,  synapse.  R,  receptor  ;  E,  effector.  (Adapted  from  Huxley-Lee.) 

to  the  cerebral  cell  may  represent  a  reaction  circuit.  It  will  be 
noted  that  the  difference  between  a  reflex  and  reaction  circuit  is 
found  in  the  fact  that  in  the  reflex  circuit  the  voluntary  centre  is 
not  involved,  or  the  resulting  action  is  involuntary,  while  in  the 
reaction  circuit  the  voluntary  centre  is  involved  and  the  resulting 
action  is  voluntary.  Volitional  centres  lie  in  the  cerebrum. 


398 


ANATOMY  AND  PHYSIOLOGY    [CHAP.  XIX 


FIG.  196.  —  DIAGRAM  TO  ILLUSTRATE 
A  SPREADING  REFLEX.  A,  axone  divid- 
ing into  terminal  branches  which  connect 
with  cells  B,  B.  These  cells  send  their 
fibres  C,  C,  C,  C,  to  supply  a  number  of 
different  muscles. 


Classification  of  reflexes.  —  In  relation  to  the  kind  of  re- 
sponse brought  about  by  a  stimulus,  reflex  circuits  may  be  classi- 
fied as :  - 

(a)  Simple  reflexes  in  which  a  single  muscle  or  gland  is  involved. 

As  an  example  of  this  group  may  be  mentioned  the  corneal  reflex. 

(6)  Complex  reflexes,  in  which  several  muscles  or  glands  are 

affected,   the  response  remaining  perfectly  coordinated   in  spite 

of  the  greater  number  of 
muscles  or  glands  affected.  The 
patellar  reflex  and  the  ankle- 
jerk  are  examples  of  this  type. 

(c)  Spreading      reflexes     in 
which  a  large  number  of  differ- 
ent muscles  are  involved. 

(d)  Tonic  or  continuous  re- 
flexes.    The  reaction  following 
a  stimulus  lasts  as  a  rule  much 
longer  than  the  stimulus.     In 
many  cases  it  becomes  tonic  in 

character.  This  result  is  frequently  obtained  when  the  nervous 
system  is  extremely  irritable  as  after  the  administration  of 
strychnine. 

(e)  Clonic  or  periodic  reflexes.  In  many  cases  a  stimulus 
may  cause  a  certain  reaction  to  be  repeated  a  number  of  times 
at  regular  intervals.  This  is  frequently  true  of  the  acts  of  sneez- 
ing, coughing,  hiccoughing,  swallowing,  and  trembling. 

(/)  Association  or  perception  reflexes.  For  some  reactions  a 
definite  mental  picture  is  the  stimulus  to  produce  the  reaction. 
Thus,  the  flow  of  saliva  or  gastric  fluid  may  be  started  when  well- 
cooked  food  is  seen  or  smelled,  or  a  person  may  find  himself  yawn- 
ing when  another  person  yawns. 

Nature  and  speed  of  nerve-impulses.  —  The  nature  of  a  nerve- 
impulse  is  not  known.  We  know  that  nerve-fibres  may  be  stimu- 
lated by  several  means,  and  the  practical  result  is  similar  to  the 
result  obtained  were  the  nerve  stimulated  by  the  natural  physio- 
logical impulse.  The  nerve-fibre  has  no  power  to  initiate  a 
nerve-impulse,  but  serves  merely  as  a  conductor  of  the  impulse 
which  has  been  started  either  in  the  end  organs  or  in  the  nerve- 
cell. 


CHAP.  XIX]  THE   NERVOUS   SYSTEM  399 

There  are  four  means  usually  applied  to  the  artificial  stimu- 
lation of  a  nerve-fibre,  viz.  chemical,  thermal,  mechanical,  and 
electrical.  The  latter  is  the  most  usual.  That  the  true  physio- 
logical impulse  is  none  of  these  can  be  readily  proven.  (See  any 
standard  work  of  physiology.) 

The  best  explanation  is  that  the  true  nature  of  a  nerve-impulse 
is  a  physical  molecular  vibration  set  up  either  in  the  nerve-cell  or 
the  end  organs  and  transmitted  along  the  nerve-fibre. 

Within  the  body  nerve-impulses  travel  in  two  directions :  (1) 
from  the  cell-body  to  the  periphery,  and  (2)  from  the  periphery  to 
the  cell-body. 

The  speed  at  which  an  impulse  travels  along  a  nerve-fibre  is 
found  to  be  about  100  to  140  feet  (27-33  m.)  per  second. 

It  may  be  interesting  to  note  how  very  slow  a  nerve-impulse  is 
when  compared  with  light  which  travels  at  the  rate  of  about 
186,000  miles  per  second,  and  sound  which  travels  about  11,000  feet 
per  second. 

Identity  of  nerve-impulses.  —  The  generally  accepted  belief  is 
that  nerve-impulses  are  identical  in  character  and  vary  only  in 
intensity.  According  to  this  the  impulses  carried  by  a  sensory 
nerve  are  similar  in  character  to  those  carried  by  a  motor  nerve, 
and  yet  the  result  is  different.  The  result  is  thought  to  be  deter- 
mined by  the  nature  of  the  centre  in  which  a  nerve-fibre  ends, 
rather  than  by  the  nature  of  the  fibre  itself. 

Reaction  of  nerve-endings.  —  A  study  of  the  previous  clas- 
sification 1  shows  that  the  sensory  nerve-endings  are  not  all 
affected  by  the  same  stimulus,  nor  do  they  react  in  the  same 
way.  Thus  some  of  the  sensory  nerve-endings  are  affected  by 
pressure,  and  others  by  temperature.  The  endings  of  the  auditory 
nerve  in  the  ear  are  affected  only  by  sound,  and  the  endings  of 
the  optic  nerve  in  the  eye  are  affected  by  sight,  though  a  similar 
effect  may  be  produced  by  a  blow  on  the  head,  or  an  accident 
which  jars  the  spinal  column. 

ANATOMY   AND    PHYSIOLOGY   OF   THE    NERVOUS 
SYSTEM 

Grouping  of  neurones.  —  The  nervous  system  is  said  to  be  com- 
posed of  gray  and  white  matter.  The  cell-bodies,  most  of  the 

1  See  page  3€, 


400 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIX 


dendrites,  and  the  commencement  of  the  axone  processes  are  not 
scattered  promiscuously  throughout  the  body,  but  are  gathered 
together  in  certain  definite  regions  or  groups.  These  form  the 
gray  matter  of  the  brain,  spinal  cord,  and  ganglia. 

The  medullated  nerve-fibres  found  in  the  brain,  spinal  corcl, 
ganglia,  and  also  in  the  nerve  trunks  distributed  to  all  parts  of 
the  body  form  the  white  matter. 

It  will  therefore  be  seen  that  the  white  matter  is  made  up  of  the 
carriers  of  nerve-impulses,  and  the  gray  matter  contains  the  cell- 
bodies  and  the  synapses  where  the  adjusting  of  sensory  to  motor 
neurones  takes  place.  For  purpose  of  study,  it  is  convenient  to 
classify  the  nervous  system  as  has  been  done  in  Chapter  III,  or 
more  simply  still  into  :  — 

1.  Vertebral  ganglia. 

2.  Collateral  ganglia. 

3.  Terminal  ganglia  and  plexuses. 

4.  Sympathetic  ganglia  in  the  brain  and  cord. 

5.  Sympathetic  nerves. 
Spinal  cord  and  spinal  nerves. 

Medulla  oblongata. 
Cerebellum. 
Pons  Varolii. 
Cerebrum. 
Cranial  nerves. 


Nervous 
System 


Sympathetic 
System 


Central 

Nervous 

System 


Brain 


THE   SYMPATHETIC   SYSTEM 

The  sympathetic  system  consists  of  four  sets  of  ganglia  and  the 
nerves  connected  with  them  :  - 

1.  Vertebral  or  lateral  ganglia. 

2.  Collateral  or  prevertebral  ganglia,  and  plexuses. 

3.  Terminal  ganglia  and  plexuses. 

4.  Sympathetic  ganglia  in  the  brain  and  cord. 

The  vertebral  ganglia.  —  The  vertebral  ganglia  consist  of  a 
chain  of  ganglia  situated  on  each  side  of  the  spinal  column,  extend- 
ing from  the  base  of  the  skull  to  the  coccyx.  (See  Fig.  197.) 
They  are  grouped  as  cervical,  thoracic,  lumbar,  and  sacral,  and 
except  in  the  neck  they  correspond  in  number  to  the  vertebrae 
against  which  they  lie  :  — 


Cervical 
Thoracic 


3  pairs 
10-12  pairs 


Lumbar 
Sacral 


4  pairs 
4-5  pairs 


CHAP.  XIX]  THE  NERVOUS   SYSTEM  401 

They  are  connected  with  each  other  by  nerve-fibres  called  ganglia 
cords,  and  with  the  spinal  nerves  by  branches  which  are  called 
rami  communicantes.  They  are  also  connected  with  the  viscera 
and  blood-vessels  by  branches  which  travel  different  pathways : 
(a)  they  pass  directly  to  the  viscera ;  (6)  they  converge  to  form 
three  main  nerve-trunks,  called  the  great  splanchnic,  the  small 
splanchnic,  and  the  least  splanchnic,  and  then  send  branches  from 
these  trunks  to  the  viscera;  (c)  they  join  the  collateral  ganglia 
and  plexuses ;  (d)  they  join  the  spinal  nerves,  by  way  of  the  gray 
rami,  and  in  them  reach  the  part  of  the  body  for  which  they  are 
destined. 

The  collateral  ganglia.  —  The  collateral  or  outlying  ganglia 
consist  of  masses  of  gray  matter  and  their  nerves,  which  are  lo- 
cated principally  in  the  thoracic  and  abdominal  cavities.  They 
are  connected  with  the  spinal  nerves,  with  the  vertebral  ganglia, 
and  send  branches  to  the  viscera.  These  branches  form  plexuses, 
the  most  important  of  which  are :  (1)  the  cardiac  plexus,  located 
above  the  heart  and  supplying  it  with  sympathetic  fibres,  (2)  the 
solar  plexus,  located  behind  the  stomach  and  supplying  most  of 
the  abdominal  viscera,  (3)  the  hypogastric  or  pelvic  plexus,  lo- 
cated in  the  lower  part  of  the  abdomen  and  supplying  the  viscera 
of  the  pelvis. 

The  terminal  ganglia.  —  The  terminal  ganglia  include  all  the 
ganglia  situated  in  the  walls  of  the  organs  themselves,  as  for  in- 
stance those  in  the  walls  of  the  heart,  and  in  the  walls  of  the  ali- 
mentary canal.  These  ganglia  are  directly  connected  with  the 
collateral  ganglia,  and  in  some  instances  the  nerves  derived  from 
the  collateral  plexuses  form  a  secondary  or  terminal  plexus  on  the 
organs. 

Sympathetic  ganglia  in  the  brain  and  spinal  cord.  —  Sympa- 
thetic ganglia  are  found  in  the  spinal  cord  and  in  the  medulla,  also 
in  connection  with  a  few  of  the  cranial  nerves,  such  as  the  third 
and  fifth.  (See  vasomotor  centre,  page  412.) 

Rami  communicantes.  —  The  nerve-fibres  that  connect  the 
vertebral  ganglia  and  the  spinal  nerves  are  called  rami  communi- 
cantes. Each  connection  consists  of  two  rami,  one  white  and  the 
other  gray.  The  white  ramus  consists  of  medullated  fibres,  and 
these  pass  from  the  spinal  cord  to  the  sympathetic  ganglion.  The 
gray  ramus  consists  of  non-medullated  fibres  that  pass  from  the 

2D 


402  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIX 

sympathetic  ganglion  to  join  the  spinal  nerve,  and  so  reach  the 
part  of  the  body  they  are  to  supply. 

Plexuses.  —  The  term  plexus  has  been  used  to  designate  a  net- 
work of  nerves.  It  is  worthy  of  special  mention  because  the  nerve- 
fibres  arborize  with  each  other,  and  there  is  an  interchange  of  fibres 
between  the  different  nerve-trunks.  The  advantages  of  this  ar- 
rangement are  :  (1)  each  nerve  is  less  dependent  on  the  unimpaired 
condition  of  any  single  portion  of  the  nerve-trunk  or  nerve  centre, 

(2)  each  nerve  has  a  wider  communication  with  the  nerve  centres, 
and  (3)  any  given  part  of  the  body  is  not  dependent  on' one  nerve. 
The  various  plexuses  of  the  sympathetic  system  serve  all  these 
purposes,  and  in  addition  the  organs  constituting  any  one  system 
are  brought  into  direct  communication  with  each  other.     In  this 
way  coordination  of  action  is  secured. 

Distribution  of  sympathetic  nerves.  —  Nerve-fibres  from  the 
sympathetic  system  are  distributed :  (1)  to  the  heart,  (2)  to  the 
involuntary  muscles  of  the  blood-vessels,  lymphatics,  and  viscera, 

(3)  to  the  secretory  glands,  and  (4)  to  some  of  the  special  senses, 
such  as  those  that  regulate  the  pupil  of  the  eye. 

Functions  of  the  sympathetic  system.  —  The  sympathetic  ner- 
vous system  exercises  a  regulatory  control  over  the  visceral  ac- 
tivities of  the  body.  Our  awareness  of  these  actions  is  limited 
as  most  of  them  are  performed  quite  unconsciously.  Nevertheless, 
they  are  of  enormous  importance  not  only  in  maintaining  our 
physical  welfare,  but  also  as  the  background  of  our  entire  conscious 
life. 

In  addition  to  the  power  of  automaticity  possessed  in  a  pre- 
eminent degree  by  the  heart  and  more  or  less  by  all  visceral  mus- 
cles, and  the  chemical  control  exercised  by  the  internal  secretions, 
the  viscera  are  under  nervous  control  of  two  sorts,  i.e.,  from  the 
sympathetic  nervous  system  and  the  central  nervous  system. 
Moreover,  the  nerves  which  carry  impulses  from  the  central 
nervous  system  to  the  viscera  are  distributed  to  the  viscera  through 
the  sympathetic  system. 

Autonomic  nervous  system.  — The  activities  controlled  by  means 
of  the  sympathetic  ganglia  are  typically  reflex  in  their  character 
and  are  relatively  independent  of  the  central  nervous  system. 
Moreover,  they  are  vegetative  or  visceral  in  their  nature  and  are 
usually  described  as  autonomic.  Accordingly,  some  authorities 


CHAP.  XIX]          THE  NERVOUS  SYSTEM  403 

use  the  term  autonomic  when  speaking  of  the  functional  side  of 
the  sympathetic  system,  while  others  apply  it  to  subdivisions  of 
the  sympathetic  system.1 

Interdependence  of  the  sympathetic  and  central  nervous  system. 
-  From  the  preceding  description  it  is  evident  that  the  sympa- 
thetic nervous  system  cannot  be  sharply  separated  either  anatomi- 
cally or  physiologically  from  the  central  nervous  system.  Ana- 
tomically the  fibres  which  connect  the  sympathetic  ganglia  and  the 
spinal  nerves  form  a  direct  pathway  from  all  of  the  viscera  to  the 
spinal  cord  and  brain.  Moreover,  many  of  the  viscera  are  con- 
nected with  the  brain  by  the  cranial  nerves.2  As  previously 
stated  the  visceral  activities  are  usually  performed  quite  uncon- 
sciously, but  it  frequently  happens  that  they  attain  conscious- 
ness. As  an  example  might  be  mentioned  the  hunger  contractions 
of  the  stomach,  or  sensations  of  pain  from  the  viscera  of  the 
abdomen,  both  of  which  show  the  functional  connection  between 
the  sympathetic  and  central  nervous  system. 

SPINAL   CORD 

A  brief  sketch  of  the  lower  animals  characterized  as  seg- 
mental,  is  helpful  in  understanding  the  structure  and  functions 
of  the  spinal  cord.  Segmental  animals  are  made  up  of  a  num- 
ber of  smaller  units  which  are  capable  of  leading  an  inde- 
pendent existence.  This  is  made  possible  by  the  fact  that 
each  segment  possesses  separate  circulatory,  digestive,  excretory, 
and  nervous  systems,  so  that  the  segments  may  be  separated 
without  endangering  or  seriously  impairing  their  life  processes. 
As  far  as  the  nervous  system  is  concerned,  we  find  that  each 
segment  of  these  animals  is  equipped  with  a  centrally  placed 
ganglion  from  which  nerve-fibres  extend  in  all  directions  to 
the  different  tissues  of  this  segment.  A  stimulus  applied  to  its 
surface  is  soon  followed  by  movement  or  some  other  motor  response. 
It  appears,  therefore,  that  the  nervous  elements  allotted  to  each 
segment  are  arranged  in  the  form  of  reflex  circuits,  their  centres 
being  grouped  in  the  shape  of  a  central  ganglion.  The  life  of  the 
animal  as  a  whole,  however,  requires  a  certain  correlation  be- 
tween the  activities  of  its  different  segments  and  a  subordination 

1  See  "  Introduction  to  Neurology  "  by  C.  Judson  Herrick.        8  See  page  421. 


404 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIX 


Sa 


UE> 


SB 


FIG.  197.  —  VENTRAL,  VIEW  OF 
BASE  OF  BRAIN,  SPINAL  CORD,  AND 
SPINAL  NERVES.  On  the  leftr-hand 
side  the  sympathetic  chain  of  ganglia 
is  shown.  V-IX,  cranial  nerves. 
Dl-D12,  Ll-L5,  S*,  S5,  and  Cocc.,  spinal 
nerves,  seen  emerging  from  spinal  cord 
by  two  roots,  with  ganglia  on  the 
dorsal  roots.  B.P.,  brachial  plexus. 
L.P.,  lumbar  plexus.  S.P.,  sacral 
plexus.  ,SV/,  S'>,  ,Vc,  cervi-al  sympa- 
thetic ganglia. 


of  the  latter  to  the  functional 
necessities  of  the  whole.  This 
end  is  attained  first  by  inter- 
mediary neurones  which  unite 
the  successive  ganglia  with  one 
another  and  secondly,  by  a  hyper- 
development  of  the  head-ganglion 
which  thus  gains  a  directing  con- 
trol over  the  others. 

A  nervous  system  of  this  kind 
is  reflex  in  its  nature  and  forms 
the  basal  stem  around  which  the 
nervous  system  as  it  appears  in 
the  highest  animals  is  eventually 
developed.  The  head-ganglion 
is  comparable  to  the  brain,  the 
segmental  ganglia  to  the  spinal 
cord,  and  from  these  parts  the 
afferent  and  efferent  nerves  arise. 

The  spinal  cord  is  that  portion 
of  the  nervous  system  lodged 
within  the  spinal  canal  of  the 
vertebral  column.  It  consists  of 
a  collection  of  gray  and  white 
substance,  extending  from  the 
foramen  magnum  of  the  skull, 
where  it  is  continuous  with  the 
medulla  oblongata,  to  about  the 
second  lumbar  vertebra,  where  it 
tapers  off  into  a  fine  thread.  Be- 
fore its  termination  it  gives  off 
a  number  of  fibres  which  form  a 
tail-like  expansion,  called  the 
cauda  equina.  (See  Fig.  21.) 

Structure  of  the  cord.  —  The 
spinal  cord  does  not  fit  closely 
into  the  spinal  canal,  as  the  brain 
does  in  the  cranial  cavity,  but 
is,  as  it  were,  suspended  within 


CHAP.  XIX]          THE  NERVOUS  SYSTEM 


405 


it.  A  series  of  spaces  intervene  between  its  surface  and  the  walls 
of  the  canal,  affording  freedom  of  movement  of  the  vertebral 
column  without  exerting  undue  tension  upon  the  cord.1  It  di- 
minishes slightly  in  size  from  above  downward,  with  the  excep- 
tion of  presenting  two  enlargements  in  the  cervical  and  lumbar 
regions,  where  the  nerves  are  given  off  to  the  arms  and  legs 
respectively.  It  varies  in  length  from  sixteen  to  twenty  inches 
(40  to  50  cm.),  and  has  an  average  diameter  of  three-fourths  of 


VENTRO-MIDIAH 


ORSAL  BOOTS 


FIG.  198.  —  TRANSVERSE  SECTION  OF  THE  SPINAL  CORD  AT  THE  MIDDLE  OF 
THE  THORACIC  REGION.  The  neuroglia  septum  has  been  removed  from  between 
the  dorsal  columns.  (Gerrish.) 

an  inch  (19  mm.).  The  spinal  cord  is  almost  completely  divided 
into  lateral  halves  by  a  ventral  and  dorsal  fissure;  the  ventral 
fissure  dividing  it  in  the  middle  line  in  front,  and  the  dorsal 
fissure  in  the  middle  line  behind.  In  consequence  of  the  pres- 
ence of  these  fissures,  only  a  narrow  bridge  of  the  substance 
of  the  cord  connects  its  two  halves.  This  bridge,  also  called  the 
isthmus,  is  traversed  throughout  its  entire  length  by  a  minute 
central  canal.  On  making  a  transverse  section  of  the  spinal  cord, 
the  gray  matter  is  seen  to  be  arranged  in  the  form  of  an  H,  and 
presents  on  each  side  a  ventral  and  dorsal  horn.  The  former  is 
short  and  bulky  while  the  latter  is  long  and  slender. 

The  transverse  bar  of  gray  matter  found  in  the  isthmus  is  called 
the  gray  commissure,  and  connects  the  two  lateral  masses  of 
gray  matter.  The  white  matter  is  arranged  around  and  between 

1  See  Membranes  of  the  Cord. 


406 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIX 


the  gray  matter,  the  proportion  of  gray  and  white  varying  in  dif- 
ferent regions  of  the  cord.  The  white  matter  is  composed  of 
medullated  nerves,  and  the  gray  matter  consists  of  cell-bodies, 
dendrites,  axones,  and  collaterals,  all  held  together  and  supported 
by  neuroglia.  The  white  matter  may  be  said  to  consist  of  three 
portions  or  funiculi,  namely,  an  anterior,  a  lateral,  and  a  posterior. 
Each  funiculus  is  in  turn  divided  into  smaller  segments  or  fascic- 
uli, commonly  called  columns  or  tracts. 

Some  of  these  tracts  consist  of  fasciculi  made  up  of  fibres  which 
are  ascending  or  sensory.     They  begin  in  the  gray  matter  of  the 


FIG.  199. — CONDUCTION  IN  SPINAL  CORD.  1,  2,  fasciculi  in  dorsal  funiculus ; 
3,  4,  5,  fasciculi  in  lateral  funiculus ;  6,  7,  fasciculi  in  ventral  funiculus  of  one  side 
of  cord.  DF,  dorsal  fissure  ;  DR,  dorsal  root ;  GM,  gray  matter  ;  SG,  spinal  gan- 
glion ;  SN,  spinal  nerve ;  VF,  ventral  fissure  ;  VR,  ventral  root.  1,  Column  of  Goll ; 
2,  column  of  Burdach ;  3,  crossed  pyramidal  tract ;  4,  Flechsig's  tract ;  5,  Gower's 
tract ;  6,  ventral  ground  bundle  ;  7,  direct  pyramidal  tract.  (Burton-Opitz.) 

cord,  ascend  and  terminate  in  the  gray  matter  of  the  brain,  e.g., 
1,  2,  4,  5  in  Fig.  199.  Other  tracts  consist  of  fasciculi  which  are 
descending  or  motor.  They  begin  in  the  gray  matter  of  the  brain, 
descend  and  terminate  in  the  gray  matter  of  the  cord,  e.g.,  3  and  7. 

Other  tracts,  e.g.,  6,  are  made  up  chiefly  of  short  ascending  and 
descending  fibres  beginning  in  one  region  of  the  spinal  cord  and 
ending  in  another. 

Membranes  of  the  cord.  —  The  spinal  cord  is  protected  and 
nourished  by  three  membranes  which  are  continuous  with  the 
membranes  covering  the  brain  and  are  called  by  the  same  names, 
viz.  (1)  pia  mater,  (2)  arachnoid,  and  (3)  dura  mater.  Surround- 
ing these  three  membranes  are  three  spaces,  called  respectively 
(a)  subarachnoid,  (6)  subdural,  and  (c)  epidural. 

(1)  The   pia   mater   closely  invests   the  entire  surface  of  the 


CHAP.  XIX]  THE  NERVOUS   SYSTEM  407 

spinal  cord.     The  subarachnoid  space  between  it  and  the  arach- 
noid membrane  contains  a  sm  ill  amount  of  cerebrospinal  fluid. 

(2)  The  arachnoid  is  a  delicate  serous  membrane  placed  between 
the  pia  mater  and  the  dura  mater.     The  subdural  space  between 
these  two  membranes  is  very  small  and  contains  just  enough 
cerebrospinal  fluid  to  moisten  their  contiguous  surfaces. 

(3)  The  dura  mater  constitutes  the  outermost  and  thickest 
sheath.     It  does  not  serve  as  a  periosteum  for  the  vertebral  bones, 
being  separated  from  them  by  the  epidural  space  which  contains 
a  certain  quantity  of  areolar  and  adipose  tissue  and  a  network  of 
veins. 

SPINAL   NERVES 

There  are  thirty-one  pairs  of  spinal  nerves,  arranged  in  the 
following  groups,  and  named  for  the  region  of  the  vertebral  column 
from  which  they  emerge. 

Cervical  8  pairs 

Thoracic 12  pairs 

Lumbar 5  pairs 

Sacral   5  pairs 

Coccygeal 1  pair 

The  first  cervical  nerve  arises  from  the  medulla  oblongata  and 
leaves  the  neural  canal  between  the  occipital  bone  and  the  atlas. 
With  this  one  exception  the  spinal  nerves  spring  from  both  sides 
of  the  spinal  cord,  and  all  except  the  coccygeal  pass  out  through 
the  intervertebral  foramina.  The  coccygeal  passes  from  the  lower 
extremity  of  the  canal. 

Mixed  nerves.  —  The  spinal  nerves  consist  almost  entirely  of 
medullated  nerve-fibres,  and  are  called  mixed  nerves  because  they 
contain  both  sensory  and  motor  fibres.  Each  spinal  nerve  has 
two  roots,  a  ventral  root  and  a  dorsal  root.  The  fibres  connected 
with  these  two  roots  are  collected  into  one  bundle,  and  form  one 
nerve  just  before  leaving  the  canal  through  the  intervertebral  open- 
ings. Before  joining  to  form  a  common  trunk,  the  fibres  connected 
with  the  dorsal  root  present  an  enlargement,  this  enlargement 
being  due  to  a  ganglion,  or  small  nerve  centre,  situated  in  the  in- 
tervertebral foramina. 

The  fibres  of  the  ventral  root  arise  from  the  gray  matter  in 
the  ventral  horn,  and  are  direct  prolongations  from  the  cell-bodies 


408 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIX 


there.  Accordingly,  all  the  fibres  making  up  the  ventral  root  are 
efferent  fibres,  and  convey  nerve-impulses  from  the  spinal  cord  to 
the  periphery. 

The  fibres  of  the  dorsal  root  arise  from  the  cells  composing  the 
enlargement  or  ganglion  of  the  dorsal  root ;  each  cell  of  the  ganglion, 
besides  sending  a  nerve-fibre  toward  the  periphery,  sends  a  branch 
along  the  dorsal  root  up  into  the  gray  matter  of  the  dorsal  horn, 
there  to  form  a  synapse  with  the  dendrites  of  other  neurones. 
The  fibres  making  up  the  dorsal  root  are  afferent  fibres,  and 
convey  nerve-impulses  from  the  periphery  to  the  spinal  cord. 

It  should  be  borne  in  mind  that  the  ventral  roots  contain  only 
motor  fibres,  and  these  have  their  origin  within  the  central  nervous 
system ;  while  the  dorsal  roots  contain  only  sensory  fibres,  and 
these  fibres  always  have  their  origin  outside  of  the  cord,  i.e.,  in 
the  spinal  ganglia. 

The  relations  of  the  roots,  fibres,  and  so  forth,  can  be  best 
understood  from  a  study  of  the  accompanying  diagrams  (Figs. 
199  and  200). 

Degeneration  and  regeneration  of  nerves.  —  Since  the  cell-body 
is  essential  for  the  nutrition  of  the  whole  cell,  it  follows  that  if 

A  B 


FIG.  200.  —  DEGENERATION  OF  SPINAL  NERVES  AND  NERVE-ROOTS  AFTER 
SECTION.  A,  section  of  nerve  trunk  beyond  the  ganglion;  B,  section  of  ventral 
root ;  C,  section  of  dorsal  root ;  D,  excision  of  ganglion ;  a,  ventral  root ;  p, 
dorsal  root ;  g,  ganglion. 

the  processes  of  a  neurone  are  cut  off,  they  will  suffer  from  malnu- 
trition and  die.  If,  for  instance,  a  spinal  nerve  be  cut,  all  the  pe- 
ripheral part  will  die,  since  the  fibres  composing  it  have  been  cut 
off  from  their  cell-bodies  situated  in  the  cord,  or  in  the  spinal 
ganglia.  The  divided  ends  of  a  nerve  that  has  been  cut  across 
readily  reunite  by  cicatricial  tissue,  —  that  is  to  say,  the  con- 
nective tissue  framework  unites,  but  the  cut  ends  of  the  fibres 


CHAP.  XIX]  THE  NERVOUS   SYSTEM  409 

themselves  do  not  unite.  On  the  contrary,  the  peripheral  or 
severed  portion  of  the  nerve  begins  to  degenerate,  the  medullary 
sheath  breaks  up  into  a  mass  of  fatty  molecules  and  is  gradually 
absorbed,  and  finally  the  axone  also  disappears.  In  regeneration, 
the  new  fibres  grow  afresh  from  the  axone  of  the  central  end  of 
the  severed  nerve-trunk,  and  penetrating  into  the  peripheral  end 
of  the  neurilemma,  grow  along  this  as  the  axone  of  the  new  nerve, 
each  axone  after  a  time  becoming  surrounded  with  a  medullary 
sheath.  Restoration  of  function  in  the  nerve  may  not  occur  for 
several  months,  during  which  time  it  is  presumed  the  new  nerve- 
fibres  are  slowly  finding  their  way  along  the  course  of  those  which 
have  been  destroyed. 

Distribution  of  the  terminal  branches  of  the  spinal  nerves.  - 
After  leaving  the  spinal  canal  each  spinal  nerve  divides  into  two 
main  trunks  known  as  the  ventral  and  dorsal  divisions.  Each 
of  these  contain  sensory  and  motor  fibres.  The  ventral  division 
supplies  the  extremities  and  parts  of  the  body  in  front  of  the  spine. 
The  dorsal  division  supplies  the  muscles  and  skin  of  the  back  of 
the  head,  neck,  and  trunk.  Each  ventral  division  connects  with 
the  sympathetic  system  by  means  of  fibres  which  pass  from  the 
nerve  to  the  sympathetic  system  and  vice  versa.  Previous  to  their 
final  distribution  in  the  cervical,  sacral,  and  lumbar  regions  these 
nerves  form  plexuses  known  as  the  cervical,  sacral,  and  lumbar 
plexuses.  In  passing  to  the  viscera,  muscles,  skin,  etc.,  these 
terminal  nerves  follow  the  same  pathway  as  the  blood-vessels. 
(See  Fig.  197.) 

Names  of  peripheral  nerves.  —  Many  of  the  larger  branches 
given  off  from  the  spinal  nerves  bear  the  same  name  as  the  artery 
which  they  accompany,  or  the  part  which  they  supply.  Thus 
the  radial  nerve  passes  down  the  radial  side  of  the  forearm,  in  com- 
pany with  the  radial  artery ;  the  intercostal  nerves  pass  between 
the  ribs  in  company  with  the  intercostal  arteries.  An  exception 
to  this  are  the  two  sciatic  nerves  which  pass  down  from  the  sacral 
plexus,  one  on  either  side  of  the  body  near  the  centre  of  each 
buttock,  and  the  back  of  each  thigh,  to  the  popliteal  region  where 
each  divides  into  two  large  branches  which  supply  the  leg  and 
foot.  Motor  branches  from  these  nerves  pass  to  nearly  all  the 
muscles  of  the  legs  and  feet  and  they  receive  sensory  branches 
from  nearly  all  parts  of  the  skin  of  the  lower  extremities. 


410  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIX 

Functions  of  the  spinal  cord :  — 

(a)  Conduction,  or  the  conveyance  of  impulses  and  sensations 
between  the  centres  and  the  periphery. 

(6)  Reflex  action,  i.e.,  the  origination  of  an  impulse  or  action 
in  response  to  stimulation  from  the  periphery,  without  of  neces- 
sity involving  the  brain  in  the  act,  or  even  without  consciousness 
of  the  reflex  act,  on  the  part  of  the  individual. 

(c)  Automatic  acts,  i.e.,  acts  set  up  primarily  in  the  cells  of 
the  cord  by  the  cells  themselves,  and  not  as  a  result  of  stimula- 
tion by  brain  cells  (voluntary  acts)  nor  as  a  result  of  peripheral 
stimulation. 

(d)  Inhibition  of  reflex  acts.  —  If  every  outside  stimulation 
were  allowed  its  full  effects  in  the  setting  up  of  reflex  acts,  the 
body  would  be  on  "the  jump  "  all  the  time.     This  overactivity 
is  checked  unconsciously  by  the  cells  of  the  spinal  cord  endowed 
with  this  function. 

(e)  Transference,   i.e.,   an   apparent  transferring  of    impulses 
from  one  set  of  fibres  to  another. 

THE    BRAIN 

The  brain  is  the  largest  and  most  complex  mass  of  nervous  tissue 
in  the  body.  It  is  contained  in  the  cavity  formed  by  the 
bones  of  the  cranium,  and  is  covered  by  three  membranes  (also 
named  meninges),  —  the  dura  mater,  pia  mater,  and  arachnoid. 

The  dura  mater  is  a  dense  membrane  of  fibrous  connective  tis- 
sue containing  a  great  many  blood-vessels.  It  is  arranged  in  two 
layers  and  the  layers  are  attached  except  in  a  few  places.  The 
external  layer  is  adherent  to  the  bones  of  the  skull,  and  forms  their 
internal  periosteum.  The  internal  layer  covers  the  brain  and 
sends  numerous  prolongations  inward  for  the  support  and  protec- 
tion of  the  different  lobes  of  the  brain.  These  projections  also 
form  sinuses  that  return  the  blood  from  the  brain,  and  sheaths 
for  the  nerves  that  pass  out  of  the  skull.  It  may  be  called  the 
protective  membrane. 

The  pia  mater  is  a  delicate  membrane  of  connective  tissue, 
containing  an  exceedingly  abundant  network  of  blood  and  lymph- 
vessels.  It  dips  down  into  all  the  crevices  and  depressions  of  the 
brain,  carrying  the  blood-vessels  which  go  to  every  part.  It  may 
be  called  the  vascular  or  nutritive  membrane. 


CHAP.  XIX]  THE   NERVOUS   SYSTEM  411 

The  arachnoid  is  a  delicate  serous  membrane  which  is  placed 
between  the  dura  mater  and  the  pia  mater.  With  the  exception 
of  the  longitudinal  fissure,  it  passes  over  the  various  eminences  and 
depressions  on  the  surface'  of  the  brain  and  does  not  dip  down  into 
them  like  the  pia  mater.  Between  the  arachnoid  and  the  pia 
mater  is  a  space  called  the  subarachnoid  space  in  which  is  a  cer- 
tain amount  of  cerebro-spinal  fluid. 

Meningeal  spaces  and  cerebro-spinal  fluid.  —  The  meningeal 
membranes  and  the  spaces  filled  with  fluid  form  a  pad  enclosing 
the  brain  and  cord  on  all  sides.  The  fluid  within  the  ventricles 
and  surrounding  the  brain  is  in  free  communication  with  that 
within  the  central  canal  of  the  cord,  and  the  spaces  surrounding 
the  cord.  Experimental  work  indicates  that  cerebro-spinal  fluid 
is  formed  in  the  ventricles  from  the  blood  and  may  be  due  to  a 
process  of  active  secretion.  The  stream  of  liquid  starts  within  the 
ventricles,  passes  out  through  foramina  into  the  subarachnoidal 
spaces,  from  which  it  is  in  turn  absorbed  by  the  veins. 

The  cerebro-spinal  fluid  is  a  thin,  watery  fluid  having  a  specific 
gravity  of  1.007  to  1.008.  It  contains  traces  of  proteins  and  other 
organic  substances.  The  normal  amount  is  difficult  to  determine 
but  is  usually  stated  as  from  60  to  80  cc.  It  may  be  formed  very 
promptly  from  the  blood,  and  when  in  excess  be  absorbed  quickly 
by  the  blood. 

Structure  of  the  brain.  —  The  whole  brain  appears  to  consist  of 
a  number  of  isolated  masses  of  gray  matter  —  some  large,  some 
small  —  connected  together  by  a  multitude  of  medullated  fibres 
(white  matter)  arranged  in  perplexing  intricacy.  But  a  general 
arrangement  may  be  recognized.  The  numerous  masses  of  gray 
matter  in  the  interior  of  the  brain  may  be  looked  upon  as  forming 
a  more  or  less  continuous  column,  and  as  forming  the  core  of  the 
central  nervous  system,  while  around  it  are  built  up  the  great 
mass  of  the  cerebrum  and  the  smaller  mass  of  the  cerebellum.  This 
central  core  is  connected  by  various  bundles  of  fibres  with  the 
spinal  cord,  besides  being,  as  it  were,  a  continuation  of  the  gray 
matter  in  the  centre  of  the  cord.  It  is  also  connected  at  its  upper 
end  by  numberless  fibres  to  the  gray  matter  on  the  surface  of  the 
cerebrum. 

Weight  of  the  brain.  —  With  the  exception  of  the  whale  and  the 
elephant,  the  human  brain  is  heavier  than  that  of  any  of  the  lower 


412  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIX 

animals.  The  average  weight  of  the  brain  in  the  male  is  49.5 
ounces  avoirdupois  (about  1485  gms.) ;  in  the  female,  44  ounces 
avoirdupois  (about  1320  gms.).  It  appears  that  the  weight  of 
the  brain  increases  rapidly  up  to  the  fifth  year  and  ceases  to  grow 
generally  in  the  eighteenth  or  twentieth  year.  After  the  sixtieth 
year  the  brain  loses  weight,  at  first  slowly,  later  more  rapidly. 

Divisions  of  the  brain.  —  The  brain  is  divided  into  four  principal 
parts :  the  cerebrum,  the  cerebellum,  the  pons  Varolii  and  the 
medulla  oblongata. 

The  medulla  oblongata.  —  The  medulla  oblongata,  also  known  as 
the  spinal  bulb,  is  continuous  with  the  spinal  cord,  which,  on  passing 
into  the  cranial  cavity  through  the  foramen  magnum,  widens  into 
an  oblong-shaped  mass.  It  is  directed  (from  above)  backward  and 
downward,  its  ventral  surface  resting  on  a  groove  in  the  occipital 
bone  and  its  dorsal  surface  forming  the  floor  of  a  cavity  between 
the  two  halves,  or  hemispheres,  of  the  cerebellum.  It  is  hollow,  and 
the  cavity,  called  the  fourth  ventricle,  is  an  expanded  continuation 
cf  the  tiny  central  canal  which  runs  throughout  the  whole  length 
of  the  spinal  cord.  The  gray  matter  is  found  in  the  interior,  and 
the  white  matter  on  the  exterior ;  most  of  the  gray  matter  is  found 
on  the  floor  of  the  fourth  ventricle,  and  from  this  gray  matter  arise 
most  of  the  cranial  nerves.  The  medulla  has  a  ventral  and  a 
dorsal  median  fissure;  at  the  lower  part  of  the  ventral  fissure 
are  nerve-fibres  which  cross  from  one  side  to  the  other  or  decussate. 

Functions  of  the  medulla  oblongata.  —  The  functions  of  the 
medulla  are  similar  to  the  first  three  listed  under  the  functions  of 
the  cord,  i.e.,  conduction,  reflex  action,  and  automatic  action. 

As  all  the  impressions  passing  between  the  brain  and  spinal  cord 
must  be  transmitted  through  the  medulla,  the  function  of  con- 
duction is  a  very  important  one.  As  previously  stated,  the  me- 
dulla contains  important  vital  and  reflex  centres.  The  principal 
ones  are :  — 

(1)  The    respiratory    centres    for    regulating    the    function    of 
respiration. 

(2)  Accelerator  centres  for  the  heart. 

(3)  Vasomotof  centre. 

Subsidiary  centres  are  also  found  in  the  spinal  cord.  The  vaso- 
motor  nerves  are  of  two  kinds,  —  vaso-oonstrictor  and  vaso-dilator. 
These  nerves  control  the  caliber  of  the  blood-vessels  and  thus  help 


CHAP.  XIX] 


THE  NERVOUS   SYSTEM 


413 


to  control  such  important  processes  as  the  circulation  of  the  blood, 
metabolism,  and  heat  regulation.  While  these  nerves  are  always 
considered  as  belonging  to  the  sympathetic  system,  it  should  be 
noted  that  the  centre  controlling  them  is  located  in  the  medulla. 
(4)  Other  centres,  e.g.,  the  vomiting  centre,  etc. 


V    r  ^'~.*i,;,  Tli        SYLVIAN 

T  ^""FISSURE 

>^T  ^       »NT«IO* 


.CEREBELLUM 


FIG.  201.  —  UNDER  SURFACE  OF  THE  BRAIN,  SHOWING  THE  SUPERFICIAL  ORIGINS 
OF  THE  CRANIAL  NERVES.     The  romaii  numerals  indicate  the  nerves.     (Gerrish.) 

The  medulla  being  the  seat  of  such  important  centres  as  those 
controlling  respiration  and  the  heart's  action,  the  student  will 
readily  appreciate  that,  if  the  medulla  be  seriously  injured,  death 
will  result. 

Cerebellum.  —  The  cerebellum,  or  "  little  brain,"  occupies  the 
lower  and  back  part  of  the  skull  cavity,  overhanging  the  medulla 
oblongata.  It  is  of  a  flattened,  oblong  shape,  and  measures 
from  three  and  a  half  to  four  inches  (8.7  to  10  cm.)  trans- 
versely, and  from  two  to  two  and  a  half  inches  (5  to  6.3  cm.) 
from  before  backward.  It  is  arbitrarily  divided  into  a  medial 
segment  called  the  vermis  and  two  lateral  lobes  or  hemispheres  ; 
each  lobe  being  subdivided  by  fissures  into  smaller  portions. 


414  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIX 

The  surface  of  the  cerebellum  consists  of  gray  matter  and  is 
traversed  by  numerous  curves,  or  furrows,  which  vary  in  depth. 
The  interior  consists  of  white  matter. 

Peduncles  of  cerebellum.  —  The  cerebellum  is  connected  with 
the  rest  of  the  cerebro-spinal  system  by  many  white  nerve  fibres 
grouped  in  bundles,  called  the  peduncles. 

The  peduncles  are  arranged  in  three  pairs  The  anterior 
(superior)  peduncles  pass  forward  from  the  cerebellum  to  enter 
into  the  cerebrum.  The  posterior  (inferior)  peduncles  pass  down 
to  the  medulla,  where  they  are  known  as  the  restiform  bodies. 
The  middle  pair  pass  into  and  make  up  the  larger  portion  of 
the  pons  Varolii,  thus  serving  as  a  means  of  intercommunication 
between  the  two  halves  of  the  cerebellum.  Thus  it  is  seen 
that  the  cerebellum  communicates  freely  with  the  entire  cerebro- 
spinal  system. 

Functions  of  the  cerebellum.  —  The  principal  function  of  the 
cerebellum  seems  to  be  the  coordination  of  ordinary  movements 
and  the  maintenance  of  equilibrium.1  The  reason  for  this  belief 
is  that  disease  or  destruction  of  the  cerebellum  apparently  exerts 
no  malign  influence  on  sensory  nerves  nor  upon  the  intellect. 
The  motor  system  is,  however,  profoundly  deranged.  Motion 
itself  is  not  destroyed,  but  coordination  is  so  interfered  with  that 
movements  of  one  part  of  the  body  cannot  be  adapted  to  other 
parts. 

Pigeons  deprived  of  the  cerebellum  will  fly  if  thrown  from  a  roof, 
but  the  delicacy  of  the  coordination  being  lost,  they  turn  a  series 
of  somersaults  in  the  air  and  soon  fall  to  the  ground. 

Pons  Varolii.  —  The  pons  Varolii,  or  bridge  of  Varolius,  lies  in 
front  of  the  upper  part  of  the  medulla  oblongata.  It  consists 
of  interlaced  transverse  and  longitudinal  white  nerve-fibres  inter- 
mixed with  gray  matter.  The  transverse  fibres  are  those  de- 
rived from  the  middle  peduncles  of  the  cerebellum  and,  as  already 
stated,  serve  to  join  its  two  halves.  The  longitudinal  fibres  join 
the  medulla  with  the  cerebrum. 

Functions  of  pons  Varolii.  —  The  pons  is  a  bridge  of  union  be- 
tween the  two  halves  of  the  cerebellum  and  a  bridge  between 
the  medulla  and  the  cerebrum.  It  is  also  a  place  of  exit  for  the 
fifth,  sixth,  seventh,  and  eighth  cranial  nerves. 

1  A  portion  of  the  inner  ear  is  also  concerned  in  maintaining  equilibrium. 


CHAP.  XIX] 


THE  NERVOUS   SYSTEM 


415 


Cerebrum.  —  The  cerebrum  is  by  far  the  largest  part  of  the 
brain.  It  is  egg-shaped,  or  ovoidal,  and  fills  the  whole  of  the 
upper  portion  of  the  skull.  The  entire  surface,  both  upper  and 
under,  is  composed  of  layers  of  gray  matter,  and  is  called  the  cortex 
because,  like  the  bark  of  a  tree,  it  is  on  the  outside.  The  bulk  of  the 
white  matter  in  the  interior  of  the  cerebrum  consists  of  very  small 
fibres  running  in  three  principal  directions  :  (1)  from  above  down- 
ward, (2)  from  the  front  backward,  and  (3)  from  side  to  side. 
The  fibres  link  the  different  parts  of  the  brain  together,  and  con- 
nect the  brain  with  the  spinal  cord. 

Fissures  and  convolutions.  —  In  early  life  the  cortex  of  the 
cerebrum  is  comparatively  smooth,  but  as  time  passes  and  the 


FIG.  202.  —  FALX  CEREBRI  AND  TENTORIUM,  LEFT  LATERAL  VIEW.     (Gerrish.) 

brain  develops,  the  surface  becomes  covered  with  depressions 
which  vary  in  depth.  The  deeper  depressions  are  called  fissures , 
the  more  shallow  ones  sulci,  and  the  ridges  between  the  sulci  are 
called  convolutions.  The  fissures  and  sulci  are  infoldings  of  gray 
matter,  consequently  the  more  numerous  and  deeper  they  are, 
the  greater  is  the  amount  of  gray  matter.  The  number  and 
depth  of  these  fissures  and  sulci  is  thought  to  bear  a  close  relation 
to  intellectual  power ;  babies  and  idiots  have  few  and  shallow 
folds,  while  the  brains  of  men  of  intellect  are  always  markedly  con- 


416  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XIX 

voluted.     There  are  five  important  fissures  which  are  always  pres- 
ent.    They  are  the  following  :  — 

(1)  The  Great  Longitudinal  Fissure,  which  extends  from  the 
back  to  the  front  of  the  cerebrum,  and  almost  completely  divides 
it  into  two  hemispheres,  the  two  halves,  however,  being  connected 
in  the  centre  by  a  broad,  transverse  band  of  white  fibres  called  the 
corpus  callosum.     A  process  of  the  dura  mater  extends  down  into 
this  fissure  and  separates  the  two  cerebral  hemispheres.     It  is 
called  the  falx  cerebri,  because  it  is  narrow  in  front,  and  broader 
behind,  thus  resembling  a  sickle  in  shape.     Blood  is  returned  from 
the   brain   in   venous   channels   called   sinuses.     Two   important 
sinuses  are  lodged  between  the  layers  of  the  falx  cerebri.     The 
superior  longitudinal  sinus  is  contained  in  the  upper  border,  and 
the  inferior  longitudinal  sinus  in  the  lower  border.     See  Fig.  202. 

(2)  The  Transverse  Fissure,  which  is  between  the  cerebrum  and 
the  cerebellum.     A  process  of  the  dura  also  extends  into  this 
fissure,  and  covers  the  upper  surface  of  the  cerebellum  and  the 
under    surface    of    the   cerebrum.      It   is   called    the   tentorium 
cerebelli. 

(3)  Fissure  of  Rolando,  or      1      ,™ 

There   is    one  of    each    in    each 

central  fissure.                            ,       .     ,  ^      , 

,..   „.             P  ^  i   -                           hemisphere,  tor  location   see 

(4)  Fissure  of  Sylvius.  2Q3 

(5)  Parieto-occipital  fissure. . 

Lobes  of  the  cerebrum.  —  The  longitudinal  fissure  divides  the 
cerebrum  into  two  hemispheres,  and  the  transverse  fissure  divides 
the  cerebrum  from  the  cerebellum.  The  three  remaining  fissures 
divide  each  hemisphere  into  five  lobes.  With  one  exception  these 
lobes  were  named  from  the  bones  of  the  cranium  under  which  they 
lie ;  hence  they  are  known  as  :  — 

(1)  Frontal  lobe. 

(2)  Parietal  lobe. 

(3)  Temporal  lobe. 

(4)  Occipital  lobe. 

(5)  Central  lobe,  or  Island  of  Reil  (the  exception) . 

(1)  The  frontal  lobe   is  that  portion   of  the  cerebrum   lying 
in  front  of  the  fissure  of  Rolando,  and  usually  consists  of  four  main 
convolutions. 

(2)  Parietal  lobe  is  bounded  in  front  by  the  fissure  of  Rolando, 
and  behind  by  the  parieto-occipital  fissure. 


CHAP.  XIX]  THE  NERVOUS   SYSTEM  417 

(3)  Temporal  lobe  lies  below  the  fissure  of  Sylvius  and  in  front 
of  the  occipital  lobe. 

(4)  Occipital  lobe  occupies  the  posterior  extremity  of  the  cerebral 
hemisphere.     When   one   examines   the   external   surface   of  the 
hemisphere,  there  is  no  marked  separation  of  the  occipital  lobe 
from  the  parietal  and  temporal  lobes  that  lie  to  the  front;    but 


-ALSO  KNOWN  AS 

FISSURE  OF  ROLANDO 


FIG.  203.  —  THE  LOBES  OF  THE   CONVEX  SURFACE   OF  THE   HEMISPHERE,  LEFT 

SIDE.     (Gerrish.) 

when  the  surface  of  the  longitudinal  cleft  is  examined,  the  parieto- 
occipital  fissure  serves  as  a  boundary  anteriorly  for  the  occipital 
lobe. 

(5)  Central  lobe,  or  Island  of  Reil,  is  not  seen  when  the  sur- 
face of  the  hemisphere  is  examined,  for  it  lies  within  the  fissure 
of  Sylvius,  and  the  overlying  convolutions  of  the  parietal  and 
frontal  lobes  must  be  lifted  up  before  the  central  lobe  comes  into 
view. 

Ventricles  of  the  brain.  —  In  describing  the  spinal  cord,  ref- 
erence was  made  to  the  central  canal,  being  a  minute  canal  running 
through  the  centre  of  the  cord  throughout  its  entire  length,  thus 
converting  the  cord  into  a  tube  with  exceedingly  thick  walls 
but  very  small  internal  caliber.  In  the  brain  proper  this  same 
central  channel  persists,  and  just  as  the  walls  or  solid  portions  of 
the  brain  are  directly  continuous  with  the  wall  or  solid  portion 
of  the  spinal  cord,  so  is  the  cavity  of  the  brain  directly  con- 

2E 


418  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIX 

tinuous  with  the  central  canal  of  the  cord.  The  cavity  in  the 
brain  presents  some  marked  differences  to  that  of  the  cord  ;  while 
the  latter  is  a  straight,  fairly  uniform  canal  of  very  small  diameter, 
the  former  is  at  some  points  very  narrow,  and  at  others  much 
widened  out  so  as  to  form  quite  good-sized  chambers,  and  these 
chambers  are  called  the  ventricles  of  the  brain.  These  ventricles 
are  filled  with  cerebro-spinal  fluid,  just  as  the  canal  of  the  cord  is 
likewise  filled  with  the  same  fluid. 

The  ventricles  are  five  in  number.  The  most  posterior  is  the 
enlargement  or  expansion  of  the  central  canal,  occupying  the  sub- 
stance of  the  medulla  oblongata,  and  is  called  the  fourth  ven- 
tricle. Leading  forward  from  the  anterior  end  of  the  fourth  ven- 
tricle, the  caliber  of  the  canal  again  narrows  to  a  very  small 
diameter ;  the  canal  on  reaching  the  brain  substance  uniting  the 
two  halves  of  the  cerebrum,  again  expands  into  a  somewhat  smaller 
chamber,  called  the  third  ventricle.  The  small  canal  already 
mentioned  as  joining  the  third  and  fourth  ventricles  is  known  as 
the  aqueduct  of  Sylvius. 

Toward  the  forward  end  of  the  third  ventricle  there  are  noted 
two  small  channels,  the  foramina  of  Monro,  one  on  either  side 
leading  in  a  direction  forward,  upward,  and  outward,  each  fora- 
men leading  into  a  very  large  ventricle  occupying  the  centre 
of  its  corresponding  cerebral  hemisphere,  called  the  lateral  ven- 
tricle. 

The  fifth  ventricle  is  very  small,  lies  between  the  two  lateral 
ventricles,  and  is^not  in  communication  with  the  other  ventricles. 

The  student  will  thus  see  that  both  the  brain  and  spinal  cord 
are  hollow.  In  some  portions,  however  (as  the  spinal  cord), 
the  interior  cavity  is  so  minute  and  the  walls  so  exceedingly 
thick  that  the  cavity  is  a  negligible  quantity,  and  the  mass 
can  practically  be  considered  as  solid ;  on  the  other  hand,  in  the 
case  of  the  ventricles,  especially  the  lateral  ventricles,  the  cavity 
is  large  enough  to  occupy  an  appreciable  space,  and  may  become 
overdistended  with  cerebro-spinal  fluid  in  certain  conditions  of 
disease. 

Functions  of  the  cerebrum.  —  The  nerve  centres  which  govern 
all  our  mental  activities  and  the  coordination  of  movements  are 
centred  in  the  cerebrum.  These  centres  are  the  seat  of  reason, 
intelligence,  will,  memory,  and  all  the  higher  emotions  and  feelings. 


CHAP.  XIX] 


THE  NERVOUS   SYSTEM 


419 


Localization  of  brain  function.  —  As  the  result  of  numerous 
experiments  on  animals,  and  close  observation  of  individuals 
suffering  from  cerebral  diseases  or  wounds,  physiologists  have  been 
able  to  localize  certain  areas  in  the  brain  which  control  motor  and 
sensory  activity.  They  have  also  been  able  to  gain  some  knowl- 
edge of  the  areas  in  the  cerebrum  which  are  concerned  with  the 
higher  mental  activities. 

Names  of  areas.  —  That  portion  of  the  cerebrum  which  governs 
muscular  movement  is  known  as  the  motor  area,  the  portions  con- 
trolling sensation  as  the  sensory  areas,  and  those  connected  with 
the  higher  faculties,  such  as  reason  and  will,  as  association  areas. 

Motor  areas.  —  The  surface  of  the  brain  assigned  to  the  func- 
tion of  motion  is  the  posterior  part  of  the  frontal  lobe,  i.e.,  the 

FISSURE  OF  ROLANDO 
OR   CENTRAL 


'B. 


FIG.  204.  —  LOCALIZATION  OF  FUNCTION  IN  THE  CEREBRAL  CORTEX.  (Adapted 
from  Woolsey's  "Surgical  Anatomy.")  The  cortical  area  marked  A  is  the  motor 
speech  centre,  damage  to  which  causes  loss  of  the  word-forming  power  (motor 
aphasia).  Damage  to  the  cortical  area  marked  B  abolishes  the  power  of  writing,  a 
form  of  sensory  aphasia  called  agraphia.  Damage  to  the  centre  marked  C  produces 
word-deafness  (sensory  aphasia) .  Damage  to  the  cortical  area  marked  D  produces 
word-blindness  (sensory  aphasia).  Stereognosis  means  the  ability  to  recognize 
the  form  of  objects  by  the  sense  of  touch. 

gray  matter  immediately  in  front  of  the  fissure  of  Rolando.  The 
movements  of  various  parts  of  the  body  are  controlled  by  nerves 
arising  in  this  area,  and  the  special  portions  of  the  area  in  which 
the  nerves  supplying  the  various  parts  arise  can  be  studied  in  Fig. 
204. 


420  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIX 

Decussation  .of  nerves.  —  The  fibres  extending  from  the  brain 
into  the  cord,  and  from  the  cord  into  the  brain,  decussate  or  cross 
in  the  medulla.  Because  of  this  it  follows  that  the  nerves  arising 
in  the  cortex  of  the  right  side  govern  the  movements  of  the  left 
side  of  the  body,  and  vice  versa. 

In  many  cases  of  paralysis  or  convulsions,  it  is  possible  to 
locate  the  exact  portion  of  the  brain  that  is  affected,  by  close  ob- 
servation of  the  part  of  the  body  involved  in  the  loss  of  function 
or  convulsion. 

Sense  areas.  —  The  term  sense  areas  is  used  to  designate 
those  parts  of  the  brain  to  which  sensation  is  due,  and  which 
control  vision,  hearing,  smell,  taste,  and  to  some  extent,  speech. 
The  visual  area  is  situated  in  the  posterior  part  of  the  occipital 
lobe ;  the  auditory  area  in  the  superior  part  of  the  temporal  lobe ; 
and  the  olfactory  and  gustatory  areas  are  in  the  anterior  part  of 
the  temporal  lobe. 

Location  of  speech  areas.  —  There  are  four  small  areas  in  the 
cerebral  cortex,  marked  A,  B,  C,  D,  in  Fig.  204  which  are  known 
as  the  speech  centres.  They  do  not  develop  in  both  hemispheres. 
In  right-handed  persons  they  become  fully  developed  in  the 
left  hemisphere,  and  in  left-handed  persons  in  the  right  hemi- 
sphere. Injury  to  these  centres  results  in  some  form  of  in- 
ability to  speak,1  to  write,2  or  to  understand,  spoken3  or 
written4  words.  It  is  customary,  therefore,  to  distinguish  two 
types  of  aphasia,  i.e.,  motor  and  sensory.  By  motor  aphasia 
is  meant  the  condition  of  those  who  are  unable  to  speak,  al- 
though there  is  no  paralysis  of  the  muscles  of  articulation.  By 
sensory  aphasia  is  meant  the  condition  of  those  who  are  unable 
to  understand  written,  printed,  or  spoken  symbols  of  words, 
although  the  sense  of  vision  and  of  hearing  are  unimpaired.  These 
centres  are  really  memory  centres  and  aphasia  is  due  to  loss  of 
memory  either  of  words,  or  the  meaning  of  words  seen  or  heard, 
or  of  how  to  form  letters.  How  these  areas  control  memory  is  not 
known.  The  basis  of  language  is  a  series  of  memory  pictures : 
(1)  of  the  sound  of  words  ;  (2)  of  their  appearance  ;  (3)  of  the  effort 
necessary  to  enunciate  them ;  and  (4)  to  write  their  symbols. 
These  memory  pictures  are  closely  related  to  each  other  by  associ- 
ation fibres  passing  between  their  centres. 

Aphasia.  2Agraphia.  3  Word-deaf  ness.  4  Word-blindness 


CHAP.  XIX]          THE  NERVOUS   SYSTEM  421 

Association  areas.. —  The  motor  and  sense  areas  previously 
outlined  form,  so  to  speak,  small  islands  which  are  surrounded  on 
all  sides  by  cerebral  tissue  in  which  as  yet  no  definite  functions 
have  been  localized.  These  unknown  regions  are  designated  as 
association  areas  and  are  supposed  to  be  set  aside  for  the  medi- 
ation of  the  various  mental  activities.  The  different  sensory  im- 
pressions are  here  moulded  into  complex  perceptions  and  concepts 
and  are  then  brought  into  relation  with  the  motor  organs. 

In  a  general  way  it  may  be  said  that  the  cerebrum  is  the  seat 
of  associations  the  sum  total  of  which  constitutes  our  psychic  life. 
In  the  absence  of  this  organ,  any  animal  must  cease  to  be  an  as- 
sociation or  reaction  animal  and  must  become  a  reflex  animal.  In 
other  words,  all  its  actions  are  then  removed  from  volition,  in 
fact,  from  consciousness.  All  responses  that  depend  upon  memory 
of  acquired  and  inherited  experience  have  been  destroyed. 

THE   CRANIAL   NERVES 

The  cranial  nerves  consist  of  twelve  pairs.  They  each  have  a 
superficial  and  a  deep  origin.  The  superficial  origin  is  the  point 
where  they  emerge  from  the  under  surface  of  the  cerebrum  and  the 
medulla,  but  they  can  be  traced  back  to  various  centres  in  the 
higher  part  of  the  brain,  and  these  centres  constitute  their  deep 
origin. 

Classification.  —  The  cranial  nerves  are  of  three  varieties : 
(1)  sensory  nerves,  (2)  motor  nerves,  and  (3)  mixed  nerves  or 
those  containing  both  sensory  and  motor  fibres.  Many  of  the 
cranial  nerves  arise  from  several  nerve  centres,  and  therefore  con- 
sist of  several  bundles  of  nerve-fibres.  After  these  nerves  leave 
the  cranium  they  split  up  into  branches  that  are  widely  distributed. 

Numbers  and  names.  —  They  are  named  numerically  according 
to  the  order  in  which  they  arise  from  the  brain,  and  also  by  names 
which  describe  their  nature,  function,  or  distribution.  The  fol- 
lowing doggerel  may  assist  the  beginner  in  learning  the  order  of 
the  cranial  nerves.  Each  capital  letter  denotes  a  cranial  nerve. 
"On  Old  Manhattan's  Peaked  Tops,  A  Finn  And  German  Picked 
Some  Hops/' 

(1)  The  olfactory  nerve  is  the  special  nerve  of  the  sense  of  smell. 
Its  origin  is  in  the  olfactory  bulb,  and  its  peripheral  fibres  are 
distributed  to  the  upper  third  of  the  nasal  cavity. 


422  ANATOMY   AND   PHYSIOLOGY     [CHAP.  XIX 

(2)  The  optic  nerve  is  the  special  nerve  of  the  sense  of  sight.     Its 
cell-bodies  are  situated  in  the  retinal  coat  of  the  eye. 

(3)  The  motor  oculi  nerve  supplies  all  the  muscles  of  the  eye 
except  the  superior  oblique  and  the  external  rectus.     It  originates 
in  the  gray  matter  of  the  pons  Varolii. 

(4)  The  pathetic,  or  trochlear,  nerve  supplies  only  the  superior 
oblique  muscle  of  the  eye.     It  arises  close  to  the  preceding  nerve. 

(5)  The  trifacial  has  two  roots,  —  a  dorsal,  or  sensory,  and  a 
ventral,  or  motor.     The  fibres  from  the  two  roots  coalesce  into  one 
trunk,  and  then  subdivide  into  three  large  branches  :   (1)  the  oph- 
thalmic, (2)  the  superior  maxillary,  and  (3)  the  inferior  maxillary. 
The  ophthalmic  branch  is  the  smallest,  and  is  a  sensory  nerve.     It 
supplies  the  eyeball,  the  lacrimal  gland,  the  mucous  lining  of  the 
eye  and  nose,  and  the  skin  and  muscles  of  the  eyebrow,  forehead, 
and  nose.     The  superior  maxillary,  the  second  division  of  the  fifth, 
is  also  a  sensory  nerve,  and  supplies  the  skin  of  the  temple  and 
cheek,  the  upper  teeth,  and  the  mucous  lining  of  the  mouth  and 
pharynx.     The  inferior  maxillary  is  the  largest  of  the  three  di- 
visions of  the  fifth,  and  is  both  a  sensory  and  a  motor  nerve.     It 
sends  branches  to  the  temple  and  the  external  ear ;  to  the  teeth  and 
lower  jaw ;    to  the  muscles  of  mastication ;    it  also  supplies  the 
tongue  with  the  special  nerve  (lingual)  of  the  sense  of  taste.  The 
cell-bodies  of  the  motor  fibres  are  situated  in  the  pons ;  while  those 
of  the  sensory  fibres,  as  in  the  case  of  the  spinal  nerves,  are  situ- 
ated in  a  ganglion.     This  ganglion  is  called  the  Gasserian  ganglion. 

(6)  The  abducens  nerve  supplies  the  external  rectus  muscle  of 
the  eye. 

(7)  The  facial  nerve  is  the  motor  nerve  of  all  the  muscles  of 
expression  in  the  face ;    it  also  supplies  the  neck  and  ear.     Its 
cells  of  origin,  like  those  of  the  abducens  nerve,  are  situated  in 
the  medulla. 

(8)  The  auditory  nerve  is  the  special  nerve  of  the  sense  of  hear- 
ing.    It  arises  from  cells  which  compose  the  organ  of  Corti  in  the 
internal  ear,  to  which  its  fibres  are  exclusively  distributed. 

(9)  The   glossopharyngeal   nerve   is   distributed,   as   its    name 
indicates,  to  the  tongue  and  pharynx,  being  the  special  nerve  of 
taste  to  part  of  the  tongue,  the  nerve  of  sensation  to  the  mucous 
membrane   of   the   pharynx,    and   of  motion   to  the  pharyngeal 
muscles. 


CHAP.  XIX]  SUMMARY  423 

(10)  The  pneumogastric  or  vagus  nerve  has  a  more  extensive 
distribution  than  any  of  the  other  cranial  nerves,  passing  through 
the  neck  and  thorax  to  the  upper  part  of  the  abdomen.     It  con- 
tains both  motor  and  sensory  fibres.     It  supplies  the  organs  of 
voice  and  respiration  with  motor  and  sensory  filaments ;   and  the 
pharynx,  oesophagus,  stomach,  and  heart  with  motor  fibres  (car- 
diac inhibitory). 

(11)  The  spinal-accessory  nerve  consists  of  two  parts :  one,  the 
spinal  portion,  and  the  other,  the  accessory  portion  to  the  tenth 
nerve.     It  is  a  motor  nerve  supplying  certain  muscles  of  the  neck. 
It  differs  from  the  other  cranial  nerves  in  arising  from  the  spinal 
cord,  but  it  leaves  the  skull  by  the  same  aperture  as  the  pneumo- 
gastric and  glossopharyngeal. 

(12)  The  hypoglossal  nerve  is  the  motor  nerve  of  the  tongue. 
Functions  of  the  nervous  system.  —  The   various   systems  of 

the  body  function  together  harmoniously  and  in  such  a  way  that 
the  individual  responds  properly  to  his  environment.  The  inter- 
pretation of  environmental  conditions  and  the  adaptive  responses 
of  the  organism  as  a  whole  to  these  conditions,  is  carried  out  by 
the  nervous  system.  It  enables  us  to  think  and  to  will,  to  recog- 
nize our  surroundings  and  to  accommodate  ourselves  to  them; 
to  move,  to  talk,  to  hear,  to  see;  and  it  guarantees  equilibrium 
and  muscular  coordination.  In  short,  it  makes  possible  all  the 
higher  functions  of  human  life. 


SUMMARY 

f  The  nervous  system  may  be  reduced  to  a  simple  unit  called  a 
Neurone  *  ,       * 

I      neurone.    The  neurone  may  be  regarded  as  the  building 

[     stone  of  the  nervous  system. 

f  Nervous  activity  of  all  kinds  may  be  reduced  to  reflex  action. 

{      The  reflex  circuit  forms  the  functional  basis  of  all  nervous 
Concept 

[     activity. 

~      .        ,  f  Receptor  or  sensory. 

1.  Consists  of  two  neurones     i  ^^ 

I  Effector  or  motor. 
Types  of 
u  1  J  Sensory  or  receptor. 

2.  Consists  of  three  neurones  \  Central  or  correlation. 
Circuits  LIT  i  /* 

[  Motor  or  effector. 

3.  Consists  of  complexes  of  above. 


424 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIX 


Synapse 


Interlacing  of  the  fine  branches  of  the  axone  of  one  neurone, 
with  the  branches  of  a  dendrite  of  another  neurone.  Not 
an  anatomical  continuation.  Nerve-impulses  are  able  to 
bridge  the  microscopic  gap. 


Reaction    f  When  cells  in  the  volitional  centres  in  the  cerebrum  enter  into 
Circuit       1     the  reflex  circuit,  it  is  spoken  of  as  a  reaction  circuit. 


Classifi- 
cation of 
Reflexes 


Nature 
and 

Speed  of 
Nerve 
Impulses 

Nerve- 
endings 


Simple. 

Complex. 

Spreading. 

Tonic  or  continuous. 

Clonic  or  periodic. 

Association  or  perception. 

Nature  not  positively  known. 
Presumably  a  physical  molecular  vibration. 
Identical  in  character,  vary  only  in  intensity. 
Speed  is  about  100  to  140  ft.  per  second. 

f  Not  all  affected  by  the  same  stimuli. 

1  Special  end  organs  to  mediate  each  sense. 


Gray 

matter 

Grouping 

of 

Neurones 

White 

matter 

Cell-bodies. 


Consists  of 


Found  in 


Found  in 


Dendrites. 

Commencement  of  axones. 
Brain. 
Spinal  cord. 
Ganglia. 
Consists  of  medullated  nerves. 
Brain. 
Spinal  cord. 
Ganglia. 
Nerve-trunks. 


Sympathetic 

System 

Nervous 

System 

Central 

Nervous 

System 

1.  Vertebral  ganglia. 

2.  Collateral  ganglia. 

3.  Terminal  ganglia  and  plexuses. 

4.  Sympathetic  ganglia  in  the  brain  and  cord. 

5.  Sympathetic  nerves. 

1.  Spinal  cord  and  spinal  nerves. 

Medulla  Oblongata. 

Cerebellum. 

Pons  Varolii. 

Cerebrum. 
3.  Cranial  nerves. 


2.  Brain 


CHAP.  XIX] 


SUMMARY 


425 


Distribu- 
tion of 
Sympa- 
thetic 
Nerves 


Chain  of  ganglia  situated  on  either  side  of  spinal 

Cervical 3  prs. 

Thoracic 10-12  prs. 

Lumbar 4  prs. 

Sacral 4-5  prs. 

1.  With  each  other  by  ganglia  cords. 

2.  With  spinal  nerves  by  rami  com- 

municantes. 

a.  Pass  directly  to  viscera. 
Great 

splanchnic. 
6.  Converge  ,  Small 

3.  With  to  form  |     splanchnic, 
viscera  I  Least 

splanchnic. 

c.  Join      collaterals      and 

plexuses. 

d.  Join  spinal  nerves. 
>rincipally  in  thoracic  and  abdominal 

With  spinal  nerves. 

With  vertebral  ganglia. 

With  viscera. 

Cardiac  plexus. 

Solar  plexus. 

Hypogastric  or  pelvic  plexus. 
Terminal  f  Located  on  walls  of  organs  themselves. 

Ganglia  {  Connected  with  collateral  ganglia. 
Sympathetic  Ganglia  are  found  in  the  medulla,  spinal  cord, 

and  in  connection  with  some  of  the  cranial  nerves. 
Sympathetic  Nerves. 

To  the  heart. 

To  the  involuntary  muscles  of  the  blood-vessels,  lymphatics, 

and  viscera. 

To  the  secretory  glands. 
[  To  some  of  the  special  senses. 


Chain  of  { 
column. 

Grouped 
as 

Vertebral 
Ganglia 

Con- 
nected 

Sympa- 
thetic 
System 

Located  p 
cavities. 

Collateral 
Ganglia 

Con- 
nected 

Form 

Function 
and 

interde- 
pendence 
of  Sym- 
pathetic 
System 


Regulatory  control  over  visceral  activities. 

The  term  autonomic  applied  to  functional  activities  of  sym- 
pathetic system. 

Sympathetic  and  central  nervous  system  are  interdependent 
both  anatomically  and  physiologically. 


426 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XIX 


Spinal 
Cord 


Spinal 
Nerves 


Brain 


Located  in  spinal  canal. 

Extends  from  foramen  magnum  to  second  lumbar  vertebra. 

Varies  in  length  from  16  to  20  inches. 

Gray  matter  in  form  of  H. 

Anterior. 

White  matter  in  funiculi 


Consists  of 


Posterior. 
Lateral. 
Fissures      I  Ventral  divides  front  portion  in  lateral  halves. 

1  Dorsal  divides  back  portion  in  lateral  halves. 
Isthmus  —  connects  lateral  halves. 
Canal  —  centre  of  isthmus. 

Pia  mater  —  inner  membrane,   closely  invests 

spinal  cord. 
Subarachnoid  space. 

Membranes  {  Arachnoid  —  middle  membrane. 
Subdural  space. 

Dura  mater  —  outer  membrane. 
Epidural  space. 

1.  Conduction. 

2.  Reflex  action. 
Functions      <  3.  Automatism. 

4.  Inhibition. 

5.  Transference. 


Number 


Variety 


Cervical 8  pairs. 

Thoracic 12  pairs. 

Lumbar 5  pairs. 

Sacral       5  pairs. 

Coccygeal 1  pair. 

31  pairs. 
Medullated. 

,T.     ,  f  Sensory. 
Mixed  <  .  ,  ,     J 
I  Motor. 


Origin  —  two  roots 

Distribution  —  two 
trunks 


/  Ventral  in  gray  matter  of  cord. 
\  Dorsal  in  spinal  ganglia. 
Ventral,  supplies  extremities,  and  parts 

of  body  in  front  of  spine. 
Dorsal,  supplies  muscles  and   skin  of 
back  of  head,  neck,  and  trunk. 


Located  in  cranial  cavity. 
Covered  by  meninges  —  same  as  spinal  cord. 
f  Medulla  Oblongata. 

Cerebellum. 
DiYinon.      {  pons  Varoli. 

Cerebrum. 


CHAP.  XIX] 


SUMMARY 


427 


Cerebro- 

spinal 

Fluid 


Found  in  meningeal  spaces  of  brain  and  cord,  central  canal 

of  cord,  and  ventricles  of  the  brain. 
Thin,  watery  fluid  formed  from  blood. 
Specific  gravity  1.007  to  1,008. 
Amount  is  about  60  to  80  cc. 


Medulla 

Oblon- 

gata 


Description 


Function 


Oblong-shaped  mass,   upward  continuation  of 

cord. 

Gray  matter  in  interior. 
White  matter  on  exterior. 
Conduction. 
Reflex  action. 
Automatism. 
Respiratory  centre. 
Accelerator  centre  for  heart. 
Vasomotor  centres  and  others. 


Cerebellum 


Pons  Varolii 


Description 


Function 


Cerebrum 


Flat  oblong-shaped  mass,  overhangs  medulla. 

3-4|  in.  transversely. 

2-2|  in.  from  before  backward. 

Gray  matter  on  exterior. 

White  matter  in  interior. 
f  Coordination. 
\  Maintenance  of  equilibrium. 

A  bridge  of  nerve-fibres  connecting  two  halves  of  cerebel- 
lum and  also  medulla  with  cerebrum. 

Egg-shaped  or  ovoidal. 
Fills  upper  portion  of  skull. 

f  Fissures. 
Gray  matter  \  „  ,  . 
,  . ,    \  Sulci. 
on  outside  I  ~.        ,  A. 

I  Convolutions. 

White  matter  on  inside. 

Great  longitudinal  fissure. 

Transverse  fissure. 

Rolandic. 

Sylvian. 

Parieto-occipital . 

Frontal. 

Parietal. 

Occipital. 

Temporal. 

Central,  or  Island  of  Reil. 

Fourth  ventricle. 

Third  ventricle. 

Lateral  ventricles  (two). 

Fifth  ventricle. 


Description 


Fissures 


Lobes 


Ventricles 


428 


ANATOMY  AND  PHYSIOLOGY    [CHAP.  XIX 


Cerebrum 


Function 


Governs  all  our  mental 
activities 


Names  of 
Areas 


Reason. 
Intelligence. 
Will. 
Memory. 
Higher  emotions. 
Movement  and  coordination  of  same- 


Motor  area  —  in  front  of  Fissure  of  Rolando. 
Visual  —  occipital  lobe. 
Auditory  —  superior   part   of   the   temporal 
lobe. 


Sense 


areas 


\  anterior  part  of  temporal  lobe. 
Gustatory  J 


Cranial  Nerves 


Association  areas  —  cerebral  tissue  surrounding  motor  and 
sense  areas,  in  which  as  yet  no  definite  functions  have 
been  localized. 


I.  Olfactory. 

II..  Optic. 

III.  Motor  oculi. 

IV.  Pathetic. 
V.  Trifacial. 

VI.  Abducens. 

VII.  FaciaL """" 

VIII.  Auditory. 

IX.  Glossopharyngeal. 

X.  Pneumogastric. 

XI.  Spinal  accessory. 

XII.  Hypoglossal. 


Functions  of 
the  Nervous 
System 


Interpretation  of  environmental  conditions  and  adap- 
tive responses  of  the  organism  as  a  whole;  makes 
possible  all  the  higher  functions  of  human  life. 


CHAPTER  XX 

INTERNAL  AND  EXTERNAL   SENSES:     TASTE,   SMELL,   HEARING, 

AND    SIGHT 

THE  sensory  nerves  which  we  have  discussed  in  the  previous 
chapter  have  their  peripheral  endings  in  receptors  or  sensory  end 
organs.  These  receptors  receive  stimuli,  transform  these  stimuli 
to  nerve-impulses  and  pass  them  on  to  the  nerves  which  carry  them 
to  centres  in  the  central  nervous  system  for  interpretation  or  for 
linkage  with  motor  nerves. 

Sense-organ.  —  A  typical  sense-organ  or  sensory  unit  consists 
of  (1)  a  peripheral  end  organ  or  receptor  which  in  most  cases  is 
constructed  so  as  to  be  responsive  only  to  a  special  form  of  stimu- 
lus, (2)  connecting  neurones  whose  only  function  is  to  conduct  the 
nerve-impulses  originating  in  the  end  organ,  and  (3)  a  centre  in 
the  nervous  system  which  interprets  and  determines  the  quality 
of  the  sensation.  In  this  connection  physiologists  use  the  phrase 
specific  nerve  energy  to  designate  the  fact  that  each  sense- 
organ  arouses  its  own  specific  quality  of  sensation,  and  no  other. 
For  example,  the  specific  energy  of  the  optic  apparatus  is  visual 
sensation,  and  of  the  auditory  apparatus  is  sound  sensation.  The 
view  generally  adopted  is  that  this  specificity  is  not  due  to  the 
end  organs  or  conducting  nerves,  but  to  the  centre  in  the  brain. 

Definition  of  sensation.  —  Sensation  is  defined  as  perception 
through  the  sense-organs,  and  is  the  result  of  stimulation  of  these 
organs.  The  sensitiveness  of  the  numerous  receptors  to  stimula- 
tion varies;  some  respond  to  a  very  mild  stimulus,  e.g.,  in  some 
parts  of  the  body  the  slightest  pressure  will  arouse  a  sensation 
while  a  similar  degree  of  pressure  in  another  part  may  fail  to  pro- 
duce any  sensation  at  all.  The  minimal  stimulus  necessary  to 
arouse  a  sensation  in  any  receptor  is  described  as  the  threshold 
stimulus  for  that  organ. 

429 


430  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 

Where  sensations  are  interpreted.  —  Sensations  are  felt  and 
interpreted  in  the  brain.  Our  habit  of  projecting  sensations  to 
the  part  that  is  stimulated,  tends  to  obscure  this  fact.  In  reality 
we  see  and  hear  with  our  brains,  because  the  eye  and  ear  serve 
only  as  end  organs  to  receive  the  stimulus  which  must  be  carried 
to  the  brain  and  interpreted  before  we  do  see  or  hear. 


CLASSIFICATION   OF   SENSATIONS 

Sensations  were  formerly  classified  into  two  groups,  i.e.,  special 
and  common.  The  special  senses  were  sight,  hearing,  touch, 
taste,  and  smell.  All  other  sensations  were  grouped  as  common. 
A  more  recent  classification  is  dependent  on  the  part  of  the  body 
to  which  the  sensation  is  projected,  and  the  two  groups  are  named  : 
(1)  internal  or  interior  senses,  and  (2)  external  or  exterior  senses. 
These  classifications  have  much  in  common,  but  differ  slightly. 

Internal  or  interior  senses.  —  The  internal  senses  are  those  in 
which  the  sensations  are  projected  to  the  interior  of  the  body. 
It  is  by  means  of  these  senses  that  we  acquire  a  knowledge  of  the 
condition  of  our  body.  Among  the  interior  senses  we  must  include 
pain,  the  sensations  from  the  semicircular  canals  and  vestibule  of 
the  internal  ear,  hunger,  thirst,  sexual  sense,  muscle  sense,  fatigue, 
and  various  obscure  sensations  which  proceed  from  the  viscera 
and  give  us  the  feeling  of  well-being  or  the  reverse,  also  the  desire 
for  defecation  or  urination. 

External  or  exterior  senses.  —  The  external  senses  are  those  in 
which  the  sensations  are  projected  to  the  exterior  of  the  body. 
They  form  the  means  by  which  we  become  acquainted  with  the 
outside  world.  They  include  pressure  and  temperature  sense, 
(heat  and  cold),  taste,  smell,  hearing,  and  sight.  Even  this  classi- 
fication is  not  absolutely  distinctive,  as  some  sensations  may  be 
projected  either  to  the  interior  or  exterior  of  the  body.  Tem- 
perature and  pain  are  examples  of  this  class. 

Cutaneous  sensation.  —  Modern  physiology  teaches  that  the 
sensory  nerves  of  the  skin  mediate  four  different  qualities  of 
sensation,  i.e.,  pressure,  cold,  heat,  and  pain.  As  a  result  the  sur- 
face of  the  skin  is  a  mosaic  of  tiny  sensory  spots  separated  by  rela- 
tively wide  intervals.  Each  spot  coincides  with  the  location  of 
some  special  end  organ  and  serves  a  specific  sense.  These  various 


CHAP.  XX]     INTERNAL  AND   EXTERNAL  SENSES      431 

spots  are  placed  either  singly  or  in  clusters.  In  some  loca- 
tions one  variety  predominates,  in  others  another.  It  is  a 
matter  of  common  knowledge  that  the  sensitiveness  of  these  va- 
rieties of  cutaneous  sensation  differs  in  different  parts  of  the  body, 
e.g.,  the  tip  of  the  finger  is  more  sensitive  to  pressure  or  contact 
than  to  alterations  of  temperature.  The  hot  and  cold  spots  and 


FIG.  205.  —  DIAGRAM  OF  COURSE  OF  CUTANEOUS  FIBRES  ON  REACHING  THE 
CORD,     (Dawson.) 

the  pressure  points  can  be  located  by  passing  a  metallic  point 
slowly  over  the  skin.  At  certain  points  a  feeling  of  contact  or 
pressure  will  be  experienced,  and  at  other  points  a  feeling  of  cold 
or  heat,  depending  on  whether  the  temperature  of  the  instrument 
is  higher  or  lower  than  that  of  the  skin. 

Classification  of  cutaneous  sensations.  —  It  has  recently  been 
suggested  that  the  cutaneous  senses  be  classified  on  the  basis  of 
the  loss  of  sensation  after  division  of  the  cutaneous  nerves  and 
the  subsequent,  gradual,  and  separate  return  of  these  sensations, 
after  suture  of  the  divided  ends.  It  has  been  found  that  the  skin 


432  ANATOMY  AND  PHYSIOLOGY      [CHAP.  XX 

is  supplied  with  two  sets  of  nerve-fibres  which  regenerate  at  dif- 
ferent times  and  these  are  named  respectively  protopathic  and 
epicritic.  The  protopathic  group  comprises  three  qualities  of 
sensation,  i.e.,  (1)  pain,  (2)  heat  above  37°  C.,  and  (3)  cold  below 
26°  C.  This  system  conveys  sensations  of  pain  and  of  extreme 
changes  of  temperature  but  the  sensibility  is  low  and  the  locali- 
zation poor.  It  is  found  in  the  viscera  and  from  a  functional 
standpoint  may  be  considered  as  a  defensive  agency  toward 
pathologic  changes.  The  epicritic  group  contains  separate  fibres 
for  heat,  cold,  light  pressures,  and  tactile  discriminations  which 
give  us  sensations  of  (1)  light  touch  and  (2)  small  differences  of 
temperature  between  26°  C.  and  37°  C.,  i.e.,  the  range  of  tempera- 
ture to  which  the  temperature  nerves  of  the  protopathic  system 
are  insensitive.  This  group  constitutes  the  special  characteristic 
of  the  skin  area  and  is  not  found  in  other  organs. 

In  addition  to  the  protopathic  fibres  the  deeper  tissues  are  sup- 
plied with  fibres  which  give  us  a  sense  of  pressure,  and  in  the  case 
of  the  muscles  and  joints,  with  fibres  which  give  us  a  knowledge 
of  the  position  of  the  movable  parts  of  the  body.  The  paths  which 
these  various  fibres  take  in  their  journey  through  the  central  ner- 
vous system  may  be  studied  in  Fig.  205. 

Pain.  —  It  is  probable  that  pain  is  the  most  widely  distributed 
sense  in  the  body.  It  is  present  throughout  the  skin  and  may  be 
aroused  by  stimulation  of  the  sensory  nerves  in  the  various  viscera 
and  membranes  of.  the  body.  Our  knowledge  of  the  physiological 
properties  of  the  end  organs  and  nerves  mediating  this  sense  is 
limited  to  the  skin.  There  is  much  evidence  to  support  the  view 
that  for  cutaneous  pain  there  exists  a  special  set  of  fibres  which 
have  a  specific  energy  for  pain.  The  pain  points  in  the  skin  are 
more  numerous  than  the  pressure  points  and  their  sensitiveness 
varies,  e.g.,  the  threshold  stimulus  for  the  cornea  is  lower  than  in 
the  case  of  the  finger  tips. 

Referred  pains.  —  Normally  we  are  able  to  localize  pain  arising 
in  the  skin,  accurately.  On  the  contrary,  pain  arising  in  the  vis- 
cera is  often  located  very  inaccurately  and  referred  to  an  entirely 
wrong  place.  The  explanation  of  this  misreference  is  that  the  pain  is 
referred  to,  or  appears  to  come  from,  the  skin  region  that  is  supplied 
with  sensory  fibres  from  the  same  spinal  segment  that  supplies  the 
organ  in  question,  and  is  due  to  a  diffusion  in  the  nerve  centres. 


CHAP.  XX]     INTERNAL  AND   EXTERNAL  SENSES      433 

Muscle  sense.  —  The  end  organs  of  the  muscle  sense  are 
situated  in  the  tendons  and  between  the  fibres  of  the  muscles. 
From  these  end  organs  afferent  fibres  carry  impulses  to  centres  in 
the  brain,  which  send  out  impulses  along  efferent  fibres  to  the 
muscles.  There  is  thus  a  circle  of  nerves  between  the  brain  and 
the  muscles,  one  nerve  giving  the  sense  of  the  condition  of  the 
muscle  to  the  brain,  and  another  carrying  the  impulse  from  the 
brain  to  the  muscle.  This  gives  us  a  certain  consciousness  of  the 
condition  of  our  muscles  at  all  times,  and  enables  us  to  coordinate 
the  contractions  of  harmonious  groups  in  order  to  produce  volun- 
tary movements. 

Hunger.  —  Hunger  occurs  normally  at  a  certain  time  after 
meals  and  is  usually  projected  to  the  region  of  the  stomach.  It 
is  presumably  due  to  contractions  of  the  empty  stomach,  which 
stimulate  the  nerves  distributed  to  the  mucous  membrane.  In 
abnormal  conditions,  e.g.,  severe  illness  and  extreme  fatigue  these 
periodic  contractions  may  be  weaker  than  usual,  or  may  not  occur 
at  all. 

Thirst.  —  This  sensation  is  projected  to  the  pharynx.  We 
know  very  little  about  the  nervous  mechanism  involved,  but  it  is 
thought  that  when  the  water  content  in  the  tissues  falls  below  a 
certain  amount,  the  sensory  nerve-fibres  in  the  pharynx  are  stimu- 
lated and  produce  the  sensation  of  thirst. 

TASTE 

Necessary  conditions.  —  Aside  from  the  conditions  which  are 
always  necessary  for  sense-perception,  —  viz.  proper  organs  for 
receiving,  communicating,  and  perceiving  the  sensory  impulse,  — 
there  must  be  present  a  sapid  substance  which  must  be  in  solu- 
tion. The  solution  in  the  case  of  dry  substances  is  effected  by 
saliva.  It  is  also  necessary  that  the  surface  of  the  organs  of  taste 
shall  be  moist.  The  substances  which  excite  the  special  sensa- 
tion of  taste,  act  by  producing  a  change  in  the  terminal  filaments 
of  the  fifth,  seventh,  and  ninth  nerves  and  this  change  furnishes 
the  required  stimulant. 

Organs  of  taste.  —  The  special  organs  of  the  sense  of  taste  are 
end  organs  of  nerve  filaments  which  are  derived  from  the  trifacial, 
facial,  and  glossopharyngeal  nerves.  These  end  organs  are  called 
taste  buds  and  are  situated  chiefly  on  the  surface  of  the  tongue, 

2F 


434  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 

though  some  are  scattered  over  the  soft  palate,  fauces,  epiglottis, 
and  even  the  vocal  cords. 

The  tongue.  —  The  tongue  is  a  freely  movable  muscular  organ 
consisting  of  two  distinct  halves  united  in  the  centre.  The  base 
or  root  of  the  tongue  is  directed  backward  and  is  attached  to  the 
hyoid  bone  by  numerous  muscles.  It  is  connected  with  the  epi- 
glottis by  three  folds  of  mucous  membrane,  and  with  the  soft 
palate  by  means  of  the  anterior  pillars  of  the  fauces. 


MUCOUS  GLANDS 


MUCOUS 


FILIFORM  PAPILLAE 


FUNGIFORM 
PAPILLAE 


FIG.  206.  —  THE  UPPER  SURFACE  OF  THE  TONGUE.     (Sappey.) 

Papilla  of  the  tongue.  —  The  tongue  is  covered  and  lined  with 
mucous  membrane.  The  mucous  membrane  on  the  under  surface 
is  similar  to  that  lining  the  rest  of  the  mouth,  but  the  mucous 
membrane  on  the  upper  surface  is  studded  with  papillae  which  pro- 
ject as  minute  prominences  and  "give  the  tongue  its  characteristic 
rough  appearance.  Of  these  papillae  there  are  three  varieties :  — 

(1)  Circumvallate  (walled  in)  papillae  are  the  largest,  are  circu- 
lar in  shape,  and  form  a  V-shaped  row  near  the  root  of  the  tongue, 
with  the  open  angle  of  the  V  turned  toward  the  lips.  They  serve  to 
secrete  mucus  and  contain  taste  buds  in  which  the  filaments  of  the 
glossopharyngeal  nerve  terminate. 


CHAP.  XX]     INTERNAL  AND   EXTERNAL  SENSES      435 

(2)  Fungiform  papillae  are  the  next  in  size,  and  are  so  named 
because  they  resemble  fungi  in  shape.     They  are  found  principally 
on  the  tip  and  sides  of  the  tongue.     Each  fungiform  papilla?  con- 
tains a  loop  of  capillaries  and  a  nerve-fibre  derived  from  the  glosso- 
pharyngeal  nerve. 

(3)  Filiform   papillae   are   the   smallest   and   most   numerous. 
They  are  found 'all  over  the  tongue,  except  at  the  root,  and  bear 
on  their  free  surface  delicate  hair-like  processes  which  seem  to  be 
specially  connected  with  the  sense  of  touch,  which  is  very  highly 
developed  on  the  tip  of  the  tongue. 

Nerve  supply  of  the  tongue.  —  The  nerve-fibres  which  terminate 
in  the  taste  buds  are  :  (1)  filaments  of  the  lingual  nerve,  which  is  a 
branch  of  the  fifth  or  trif acial,  (2)  filaments  of  the  chorda  tympani, 
a  branch  of  the  seventh  or  facial,  and  (3)  filaments  of  the  ninth 
or  glossopharyngeal  nerve.1  The  twelfth  or  hypoglossal  nerve  is 
distributed  to  the  tongue,  but  is  a  motor  nerve  and  is  not  con- 
cerned in  the  sense  of  taste  or  touch. 

Other  sensations  in  the  tongue.  —  The  sense  of  touch  is  very 

highly  developed  here,  and  with  it  the  sense  of  temperature,  pain, 

etc.      Upon  these  tactile  and  muscular  senses  to  a  great  extent 

depend  the  accuracy  of  the  tongue  in  many  of  its  important  uses 

—  speech,  mastication,  deglutition,  sucking. 

We  often  confound  taste  with  smell.  Substances  which  have 
a  strong  odor,  such  as  onions,  are  smelled  as  we  hold  them  in  our 
mouths ;  and  if  our  sense  of  smell  is  temporarily  suspended,  as  it 
sometimes  is  by  a  bad  cold  in  the  head,  we  may  eat  garlic  and 
onions  and  not  taste  them.  Hence  the  practice  of  holding  the 
nose  when  we  wish  to  swallow  a  nauseous  dose. 

SMELL 

Necessary  conditions.  —  The  first  essentials  are  a  special  nerve 
and  nerve-centre,  the  changes  in  whose  condition  are  perceived 
as  sensations  of  odor.  No  other  nerve  structure  is  capable  of 
such  sensations,  even  when  acted  on  by  the  same  cause.  The 
special  organs  for  this  sense  must  be  in  their  normal  condition, 
and  a  stimulus  (odor)  must  be  present  to  excite  them. 

Odors  are  caused  either  by  minute  particles  of  solid  matter  or 

1  This  is  the  generally  accepted  view,  but  other  statements  may  be  found  in  the 
various  text-books. 


436 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 


by  gases  which  are  in  the  atmosphere,  and  they  must  be  capable 
of  solution  in  the  mucus  of  the  pituitary  1  membrane.  Odorous 
particles  in  the  air,  passing  through  the  lower,  wider  air  passages, 
pass  by  diffusion  into  the  higher,  narrower,  nasal  chambers, 
and  falling  on  the  membrane  which  is  provided  with  olfactory 
nerve-endings,  produce  sensory  impulses  which,  ascending  to 
the  brain,  give  rise  to  the  sensation  of  smell. 

If  we  wish  to  smell  anything  particularly  well,  we  sniff  the  air 
up  into  the  higher  nasal  chambers,  and  thus  bring  the  odorous 
particles  more  closely  into  contact  with  the  olfactory  nerves. 


OLFACTORY 
NERVE 


BRANCH  OF 
FIFTH  NERVE 


MIDDLE 
TURBINATE 


INFERIOR 
TURBINATE 


HARD  PALATE 


FIG.  207.  —  VERTICAL  LONGITUDINAL  SECTION  OF  NASAL  CAVITY. 

Each  substance  we  smell  causes  its  own  particular  sensation, 
and  we  are  not  only  able  to  recognize  a  multitude  of  distinct 
odors,  but  also  to  distinguish  individual  odors  in  a  mixed  smell. 
The  sensation  takes  some  time  to  develop,  after  the  contact  of 
the  odorous  stimulus,  and  may  last  a  long  time.  When  the  stim- 
ulus is  repeated,  the  sensation  very  soon  dies  out,  the  sensory 
terminal  organs  quickly  becoming  exhausted.2 

Olfactory  nerves.  —  The  olfactory  nerves  are  the  special  nerves 
of  the  sense  of  smell,  and  are  spread  out  in  a  fine  network  over 

1  This  name  is  given  to  the  membrane  that  lines  the  nasal  passages. 

2  This  accounts  for  the  fact  that  one  may  easily  become  accustomed  to  foul  odors, 
and  is  of  special  importance  to  nurses.     Foul  odors  are  quickly  noticed  by  any 
one  coming  into  a  sick  room  from  out  of  doors,  but  a  nurse  who  is  in  the  sick  room 
constantly  may  become  accustomed  to  such  odors.     Hence  the  importance  of  act- 
ing on  the  first  sensation  of  a  disagreeable  odor. 


CHAP.  XX]     INTERNAL  AND  EXTERNAL  SENSES      43* 

the  surface  of  the  superior  turbinated  processes  of  the  ethmoid 
bone  and  on  the  upper  third  of  the  septum.  The  nerves  end  in 
special  organs  known  as  olfactory  cells,  which  lie  under  the  epithe- 
lium, but  send  prolongations  between  the  mucous  cells  to  the  sur- 
face. The  central  portions  of  the  olfactory  cells  are  prolonged 
as  nerve-fibres  into  a  mass  of  gray  matter,  called  the  olfactory  bulb, 
which  rests  upon  the  cribriform  plate  of  the  ethmoid  bone. 

The  nerves  which  ramify  over  the  lower  part  of  the  lining 
membrane  of  the  nasal  cavity  are  branches  of  the  fifth  or  tri- 
geminal  nerve.  These  nerves  furnish  the  tactile  sense  and  enable 
us  to  perceive,  by  the  nose,  the  sensations  of  cold,  heat,  tickling, 
pain,  and  tension  or  pressure.  It  is  this  nerve  which  is  affected 
by  strong  irritants,  such  as  ammonia  or  pepper. 

HEARING 

The  auditory  apparatus  consists  of :  (1)  the  external  ear ;  (2) 
the  middle  ear ;  (3)  the  internal  ear ;  and  (4)  the  auditory  nerve. 

External  ear.  —  The  external  ear  consists  of  an  expanded  por- 
tion named  pinna,  or  auricle,  and  the  auditory  canal,  or  meatus. 

The  auricle,  except  the  lower  portion,  consists  of  a  frame- 
work of  cartilage,  containing  some  fatty  tissue  and  a  few  muscles. 
In  the  lower  portion,  which  is  called  the  lobe,  the  cartilage  is 
replaced  by  connective  tissue.  The  auricle  is  covered  with  skin, 
and  joined  to  the  surrounding  parts  by  ligaments  and  a  few  muscles. 
It  is  very  irregular  in  shape,  and  appears  to  be  an  unnecessary 
appendage  to  the  organ  of  hearing,  except  that  the  central  depres- 
sion, the  concha,  serves  to  some  extent  to  collect  sound-waves, 
and  to  conduct  them  into  the  auditory  canal. 

The  auditory  canal  is  a  tubular  passage,  about  an  inch  (2.5  cm.) 
in  length,  leading  from  the  concha  to  the  drum-membrane.  The 
exterior  portion  of  the  wall  of  the  auditory  canal  consists  of  carti- 
lage, which  is  continuous  with  that  of  the  auricle;  the  posterior 
portion  is  hollowed  out  of  the  temporal  bone.  This  canal  is  slightly 
curved  upon  itself  so  as  to  be  higher  in  the  middle  than  at  either 
end,  and  its  direction  is  forward  and  inward.  Lifting  the  auricle 
upward  and  backward  tends  to  straighten  the  canal ;  except  in  the 
case  of  children  it  is  best  straightened  by  drawing  the  auricle 
downward  and  backward.  It  is  lined  by  a  prolongation  of  the 
skin,  which  in  the  outer  half  of  the  canal  is  very  thick  and  not  at 


438 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 


all  sensitive,  and  in  the  inner  half  is  thin  and  highly  sensitive. 
Near  the  orifice  the  skin  is  furnished  with  a  few  hairs,  and  far- 
ther inward  with  modified  sweat-glands,  the  ceruminous  glands, 
which  secrete  a  yellow,  pasty  substance  resembling  wax.  This 
wax  is  thought  to  be  offensive  to  insects,  and  consequently  a  de- 
fence against  their  intrusion. 


FIG.  208.  —  SEMI-DIAGRAMMATIC  SECTION  THROUGH  THE  RIGHT  EAR.  M , 
concha ;  G,  the  external  auditory  canal ;  T,  tympanic,  or  drum-membrane ;  P, 
tympanum,  or  middle  ear  ;  o,  oval  window  ;  r,  round  window.  Extending  from  T 
to  o  is  seen  the  chain  of  the  tympanic  bones ;  R,  Eustachian  tube ;  V,  B,  S,  bony 
labyrinth  ;  V,  vestibule  ;  B,  semicircular  canal ;  S,  cochlea  ;  b,  I,  v,  membranous 
labyrinth  in  semicircular  canal  and  in  vestibule.  A,  auditory  nerve  dividing  into 
branches  for  vestibule,  semicircular  canal,  and  cochlea, 

Middle  ear.  —  The  middle  ear,  or  tympanum,  is  a  small,  ir- 
regular bony  cavity,  situated  in  the  petrous  portion  of  the  tem- 
poral bone,  and  lined  with  mucous  membrane.  It  is  separated 
from  the  external  auditory  canal  by  the  drum-membrane  (mem- 
brana  tympani),  and  from  the  internal  ear  by  a  very  thin,  bony 
wall  in  which  there  are  two  small  openings  covered  with  mem- 
brane —  the  oval  window,  or  fenestra  ovalis,  and  the  round  win- 
dow, or  fenestra  rotunda.  The  cavity  of  the  middle  ear  is  so  small 
that  probably  five  or  six  drops  of  water  would  completely  fill  it. 


CHAP.  XX]     INTERNAL  AND   EXTERNAL  SENSES      439 

It  communicates  below  with  the  pharynx  by  the  small  passage 
called  the  Eustachian  tube.1 

The  function  of  the  tube  is  to  ventilate  this  cavity  and  keep  the 
atmospheric  pressure  equal  on  each  side  of  the  drum-membrane. 
The  middle  ear  also  communicates  with  a  number  of  bony 
cavities  in  the  mastoid  portion  of  the  temporal  bone.  These 
cavities,  called  mastoid  cells,  are  lined  with  mucous  membrane, 
which  is  continuous  with  that  covering  the  cavity  of  the  tympa- 
num. 

Membrana  tympani  (membrane  of  the  drum) .  —  It  is  a  tough, 
fibrous  membrane  set  in  the  bony  opening  of  the  external  audi- 


MALLEUS 


HORT  PROCESS 
OF   INCUS 


LONG  PROCESS 
OF  INCUS 


TMALLEUS   LONG  PROCESS        HANDLE         STAPES 

STAPES  OF  MALLEUS  OF  MALLEUS 

FIG.  209.  —  OSSICLES  OF  THE  TYMPANUM,  X  4.     (Flint.) 

tory  canal.  The  degree  of  tension  of  the  membrane  is  regulated 
by  the  tensor  tympani  muscle.  This  muscle  is  lodged  in  a  bony 
canal  that  is  above  and  parallel  with  the  Eustachian  tube. 

Ossicles.^  —  Stretching  across  .the  tympanic  cavity  is  a  chain 
of  tiny,  movable  bones,  three  in  number,  and  named  from  their 
shape  the  malleus,  or  hammer,  the  incus,  or  anvil,  and  the  stapes, 
or  stirrup.  The  handle  of  the  hammer  is  attached  to  the  drum- 
membrane,  and  the  opposite  end  or  head  of  the  hammer  is  at- 
tached to  the  base  of  the  anvil.  The  long  process  of  the  anvil  is 
attached  to  the  stapes,  and  the  footpiece  of  the  stapes  is  attached 
to  the  fibrous  membrane  that  is  stretched  across  the  oval  window. 

1  This  direct  connection  between  the  ear  and  the  pharynx  is  one  of  the  important 
reasons  for  the  frequent  cleansing  of  the  mouth  necessary  in  infectious  diseases. 
The  Eustachian  tube  forms  a  passageway  for  germs  to  travel  from  the  mouth  to  the 
middle  ear  and  there  cause  various  infections. 


440  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 

These  little  bones  are  held  in  position,  attached  to  the  drum-mem- 
brane, to  each  other,  and  to  the  membrane  of  the  oval  window  by 
minute  ligaments  and  muscles.  They  are  set  in  motion  with  every 
movement  of  the  drum-membrane.  Vibrations  of  the  mem- 
brane are  communicated  to  the  hammer,  taken  up  by  the  anvil, 
and  transmitted  to  the  stirrup,  which  rocks  in  the  fenestra  ovalis, 
and  is  therefore  capable  of  transmitting  to  the  fluid  in  the  cavity 
of  the  labyrinth  the  impulses  which  it  receives. 

Internal  ear.  —  The  internal  ear,  or  labyrinth,  receives  the  ulti- 
mate terminations  of  the  auditory  nerve,  and  is,  therefore,  the 
essential  part  of  the  organ  of  hearing.  It  consists  of  a  bony 
labyrinth,  which  is  composed  of  a  series  of  peculiarly  shaped 
cavities,  hollowed  out  of  the  petrous  portion  of  the  temporal 
bone,  and  named  from  their  shape :  — 

(a)  The  vestibule. 

(6)  The  semicircular  canals. 

(c)  The  cochlea  (snail-shell). 

Within  the  bony  labyrinth  is  a  membranous  labyrinth,  having 
the  same  general  form  as  the  cavities  in  which  it  is  contained 
though  considerably  smaller,  being  separated  from  the  bony  walls 
by  a  quantity  of  fluid  called  the  perilymph.  It  does  not  float 
loosely  in  this  liquid  because  in  some  places  it  is  attached  to  the 
bone  by  bands  of  fibrous  tissue.  The  cavity  within  the  membrane 
is  filled  with  a  fluid  called  endolymph. 

The  vestibule  is  the  central  cavity  situated  between  the  cochlea 
in  front  and  the  semicircular  canals  behind.  It  communicates 
with  the  middle  ear  by  means  of  the  oval  window  in  its  outer  wall. 
The  vestibular  membrane  does  hot  conform  to  the  shape  of  the 
bony  cavity  but  consists  of  two  small  sacs,  called  respectively  the 
saccule  and  the  utricle.  The  saccule  is  in  front  and  nearer  the 
cochlea,  and  the  utricle  is  back  and  nearer  the  semicircular  canals. 
These  sacs  are  connected  by  a  tube  called  the  endolymph  duct, 
which  is  shaped  like  a  Y.  The  walls  of  these  sacs  contain  nu- 
merous columnar  cells  provided  with  stiff  hairs  which  project  into 
the  endolymph.  These  cells  are  in  relation  with  fibres  of  the  ves- 
tibular branch  of  the  auditory  nerve  and  serve  as  end  organs. 
Among  these  hair-cells  rest  several  small  crystals  of  calcium  car- 
bonate which  are  called  otoliths. 


CHAP.  XX]     INTERNAL  AND   EXTERNAL  SENSES     441 

The  cochlea  opens  from  the  front  end  of  the  vestibule  and  sac- 
cule.  It  resembles  a  snail-shell  and  consists  of  a  spiral  tube  of 
two  and  one-half  turns  around  a  central  pillar  called  the  modiolus. 

Projecting  from  the  modiolus  is  a  thin  lamina  or  plate  of  bone. 
At  its  outer  margin  this  lamina  connects  with  a  membrane  which 
extends  to  the  outer  wall  of  the  cochlea.  This  lamina  and  mem- 
brane divide  the  spiral  canal  into  two  passages  or  scalse.  The 
lower  portion  of  this  membrane  is  called  the  basilar  membrane 


FIG.  210.  —  THE  LEFT  BONY  LABYRINTH  OF  A  NEW-BORN  CHILD,  FORWARD  AND 
OUTWARD  VIEW,  X  4. 

1,  the  wide  canal,  the  beginning  of  the  spiral  canal  of  the  cochlea ;  2,  the  fenestra 
rotunda ;  3,  the  second  turn  of  the  cochlea ;  4,  the  final  half-turn  of  the  cochlea ; 
5,  the  border  of  the  bony  wall  of  the  vestibule,  situated  between  the  cochlea  and 
the  semicircular  canals ;  6,  the  superior,  or  sagittal  semicircular  canal ;  7,  the 
portion  of  the  semicircular  canal  bent  outward ;  8,  the  posterior,  or  transverse 
semicircular  canal ;  9,  the  portion  of  the  posterior  connected  with  the  superior  semi- 
circular canal ;  10,  point  of  junction  of  the  superior  and  the  posterior  semicircular 
canals ;  11,  the  ampulla  ossea  externa ;  12,  the  horizontal,  or  external  semicircular 
canal.  (Flint.) 

and  consists  of  a  network  of  fibres  which  forms  the  foundation  for 
thousands  of  cells  which  serve  as  the  end  organs  of  the  auditory 
nerve.  These  end  organs  constitute  a  structure  that  is  known  as 
the  organ  of  Corti.  They  receive  nerve-fibres  which  arise  in  the 
ganglia  contained  in  the  cavity  of  the  modiolus.  Both  the  modio- 
lus and  lamina  are  pierced  by  numerous  openings  for  the  passage 
of  these  nerves. 

The  semicircular  canals  are  three  bony  canals  lying  above  and 
behind  the  vestibule,  and  communicating  with  it  by  five  openings, 
in  one  of  which  two  tubes  join.  They  are  known  as  the  posterior, 


442  ANATOMY  AND   PHYSIOLOGY       [CHAP.  XX 

vertical,  and  horizontal  canals,  and  their  position  is  such  that  each 
one  is  at  right  angles  to  the  other  two.  One  end  of  each  tube  is 
enlarged  and  forms  what  is  known  as  the  ampulla.  The  membrane 
of  the  ampulla  is  covered  with  cells  that  are  similar  to  those  found 
in  the  utricle  and  saccule.  These  hair-cells  serve  as  end  organs 
for  the  vestibular  branch  of  the  auditory  nerve. 

The  auditory  nerve.  —  The  eighth  or  auditory  nerve  is  a  sensory 
nerve  and  contains  two  distinct  sets  of  fibres,  which  differ  in  their 
function,  origin,  and  destination.  One  set  of  fibres  is  known  as 
the  cochlear  division  and  the  other  as  the  vestibular. 

The  fibres  of  the  cochlear  nerve  arise  from  bipolar  cells  that  are 
situated  in  the  modiolus  of  the  cochlea.  One  axone  frem  each 
cell  passes  through  the  foramina  of  the  modiolus  or  lamina,  and 
terminates  in  and  around  the  cells  that  constitute  the  organ  of 
Corti.  The  other  axone  passes  through  the  internal  auditory 
meatus  to  a  portion  of  the  brain,  called  the  cochlear  root  of  the 
auditory  nerve.  This  root  is  located  at  the  lower  edge  of  the  pons 
Varolii.  The  nerve-fibres  which  pass  from  the  ear  to  the  pons 
or  from  the  pons  to  the  ear  are  not  continuous  strands,  as  there 
are  several  relays  of  ganglia  in  which  the  axones  of  one  cell  inter- 
lock with  the  dendrites  of  another  cell. 

The  fibres  of  the  vestibular  nerve  have  their  origin  in  the  gray 
matter  of  the  pons  Varolii.  Some  of  these  fibres  extend  to  the 
cerebellum  and  to  motor  centres  of  the  spinal  nerves.  Other 
fibres  extend  to  the  vestibule  and  are  distributed  around  the  hair- 
cells  of  the  saccule,  utricle,  and  the  ampulla  of  the  semicircular 
canals. 

Physiology  of  hearing.  —  All  bodies  which  produce  sound  are 
in  a  state  of  vibration,  and  communicate  their  vibrations  to  the 
air  with  which  they  are  in  contact. 

When  these  air-waves,  set  in  motion  by  sonorous  bodies,  enter 
the  external  auditory  canal,  they  set  the  drum-membrane  vibrat- 
ing ;  stretched  membranes  taking  up  vibrations  from  the  air  with 
great  readiness.  These  vibrations  are  communicated  to  the  chain 
of  tiny  bones  stretched  across  the  middle  ear,  and  their  oscilla- 
tions cause  the  membrane  leading  into  the  internal  ear  to  be 
alternatively  pushed  in  and  drawn  out ;  the  vibrations  are  in  this 
way  transmitted  to  the  perilymph.  The  movements  of  the  peri- 
lymph  are  transmitted  to  the  basilar  membrane,  and  set  some  of 


CHAP.  XX]     INTERNAL  AND  EXTERNAL  SENSES      443 


the  strings  in  motion.  In  some  unknown  way  these  movements 
are  transmitted  to  the  hair-cells  and  through  them  to  the  nerve- 
fibres  at  their  base.  By  means  of  the  nerve-fibres  the  stimulus 
is  conveyed  to  the  brain  and  interpreted  there,  so  that  it  is  with 
the  brain  we  hear. 

The  sense  of  equilibrium.  —  Among  the  various  means  (such 
as  sight,  touch,  and  muscular  sense)  whereby  we  are  enabled  to 
maintain  our  equilibrium,  coordinate  our  movements,  and  become 
aware  of  our  position  in  space,  one 
of  the  most  important  is  the  action 
of  the  vestibule  and  semicircular 
canals.  Though  these  structures  are 
found  in  the  inner  ear  and  com- 
municate with  the  cochlea,  it  is  now 
thought  that  they  are  not  connected 
with  the  sense  of  hearing.  Just  how 
they  perform  their  function  is  not 
known,  but  it  is  thought  that  move- 
ments of  the  head  set  up  movements 
in  the  endolymph  of  the  canal,  and 
these  act  as  a  stimulus  to  the  nerve- 
endings  around  the  hair-cells. 

The  canals  are  so  arranged  (Fig.  211)  that  any  movement  of 
the  head  causes  an  increase  in  the  pressure  of  the  endolymph  in  one 
ampulla,  and  a  corresponding  diminution  in  the  ampulla  of  the 
parallel  canal  on  the  opposite  side.  Thus,  a  nodding  of  the  head 
to  the  right  would  cause  a  flow  of  the  endolymph  from  a  to  b  in 
the  right  anterior  vertical  canal,  but  from  &'  to  a'  in  the  left  poste- 
rior vertical  canal.  Hence  the  pressure  upon  the  hairs  is  de- 
creased in  a,  but  increased  in  a'.  Such  stimulations  of  the  sen- 
sory hairs  are  transmitted  by  the  dendrites  of  the  vestibular  nerve, 
through  the  cell-bodies  of  the  vestibular  ganglion  and  the  axones 
of  the  auditory  nerve,  to  the  pons  Varolii  and  thence  to  the  cere- 
bellum. It  is  thought  that  the  cerebellum  is  the  centre  in  the 
brain  which  interprets  and  adjusts  the  impulses  that  arise  from 
stimulation  of  the  sensory  nerves  concerned  with  muscular  sense. 
It  is  also  the  centre  that  interprets  and  adjusts  impulses  that  arise 
from  stimulation  of  the  vestibular  nerve-endings.  From  this  it 
follows  that  the  cerebellum  controls  equilibrium. 


FIG.  211.  —  DIAGRAM  SHOW- 
ING RELATIVE  POSITION  OF  THE 
PLANES  IN  WHICH  THE  SEMI- 
CIRCULAR  CANALS  LIE. 
Rt.,  right  ear;  Lt.,  left  ear; 
A.V.,  anterior  vertical  canal; 
P.V.,  posterior  vertical  canal; 
H.,  horizontal  canal ;  a,  am- 
pulla of  Rt.  anterior  vertical 
canal ;  a',  ampulla  of  Lt.  pos- 
terior vertical  canal. 


444  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 

SIGHT 

The  visual  apparatus  consists  of  the  eyeballs,  the  optic  nerves, 
and  the  nerve  centres  in  the  brain.  In  addition  to  these  essential 
organs,  there  are  accessory  organs  which  are  necessary  for  the 
protection  and  functioning  of  the  eyeball. 

Accessory  organs  of  the  eye.  —  Under  this  heading  we  class : 
(1)  eyebrows,  (2)  eyelids,  (3)  lacrimal  apparatus,  and  (4)  muscles 
of  the  eyeball. 

Eyebrows.  —  The  eyebrows  are  two  thickened  ridges  of  skin, 
covered  with  hairs.  They  are  situated  on  the  upper  border  of  the 
orbits,  and  protect  the  eyes  from  too  vivid  light. 

Eyelids.  —  The  eyelids  are  two  folds  projecting  from  above  and 
below  in  front  of  the  eye.  They  are  covered  externally  by  the 
skin,  and  internally  by  a  mucous  membrane,  the  conjunctiva, 
which  is  reflected  from  them  over  the  globe  of  the  eye.  They 
are  composed  for  the  most  part  of  connective  tissue,  which  is 
dense  and  fibrous  under  the  conjunctiva,  where  it  is  known  as 
the  tar  sal  cartilage. 

Arranged  in  a  double  or  triple  row  at  the  margin  of  the  lids 
are  the  eyelashes;  those  of  the  upper  lid  more  numerous  and 
longer  than  those  of  the  lower.  The  upper  lid  is  attached  to  a 
small  muscle  which  is  called  the  elevator  of  the  upper  lid  (levator 
palpebrce  superioris) ,  and  arranged  as  a  sphincter  around  both 
lids  is  the  orbicularis  palpebrarum  muscle,  which  closes  the  eye- 
lids. 

The  slit  between  the  edges  of  the  lids  is  called  the  palpebral 
fissure.  It  is  the  size  of  this  fissure  which  causes  the  appearance 
of  large  and  small  eyes,  as  the  size  of  the  lobe  itself  varies  but 
little.  The  outer  angle  of  this  fissure  is  called  the  external  can- 
thus;  the  inner  angle,  the  internal  canthus. 

The  eyelids  are  obviously  provided  for  the  protection  of  the 
eye;  movable  shades  which  by  their  closure  exclude  light,  par- 
ticles of  dust,  and  other  injurious  substances. 

Tarsal  glands  (Meibomian  glands) .  —  Embedded  in  the  tarsal 

cartilage  of  each  eyelid  is  a  row  of  elongated  sebaceous  glands, 

—  the  tarsal  *  glands,  —  the  ducts  of  which  open  on  the  edge  of 

1  By  everting  the  eyelids,  these  glands  may  be  seen  through  the  conjunctiva 
lying  in  parallel  rows. 


CHAP.  XX]     INTERNAL   AND   EXTERNAL   SENSES      445 


the  eyelid.     The  secretion  of  these  glands  prevents  adhesion  of 
the  eyelids. 

Lacrimal  apparatus.  —  This  apparatus  consists  of :  (1)  the 
lacrimal  gland,  (2)  canaliculi,  (3)  lacrimal  sac,  and  (4)  nasal 
duct. 

The  lacrimal  gland  is  a  compound  gland,  and  is  lodged  in  a  de- 
pression at  the  upper  and  outer  angle  of  the  orbit.  It  consists  of 
two  portions,  an  upper 
portion  about  the  size 
and  shape  of  an  almond, 
and  a  lower  portion  con- 
sisting of  a  group  of  small 
glands  arranged  in  a  row. 
These  two  portions  are 
only  partially  separated 
by  a  fibrous  septum. 

Seven  to  twelve  minute 
ducts  lead  from  the  gland 
to  the  surface  of  the  con- 
junctiva of  the  upper  lid. 
The  secretion  (tears)  is 
usually  just  enough  to 
keep  the  eye  moist,  and 
after  passing  over  the 
surface  of  the  eyeball  is  sucked  into  two  tiny  canaliculi  through 
the  punctce  and  is  conveyed  into  the  lacriihal  sac,  which  is  the 
upper  dilated  portion  of  the  nasal  duct. 

The  nasal  duct  is  a  membranous  canal,  about  three-quarters 
of  an  inch  (1.9  cm.)  in  length,  which  extends  from  the  lacrimal 
sac  to  the  nose,  into  which  it  opens,  by  a  slightly  expanded  orifice. 

The  tears  consist  of  water  containing  a  little  salt  and  albumin. 
They  are  ordinarily  carried  away  as  fast  as  formed,  but  under 
certain  circumstances,  as  when  the  conjunctiva  is  irritated,  or 
when  painful  emotions  arise  in  the  mind,  the  secretion  of  the 
lacrimal  gland  exceeds  the  drainage  power  of  the  nasal  duct, 
and  the  fluid,  accumulating  between  the  lids,  at  length  overflows 
and  runs  down  the  cheeks. 

The  conjunctiva.  —  The  conjunctiva  is  the  mucous  membrane 
which  lines  the  eyelids  and  is  reflected  over  the  front  of  the  eyeball. 


FIG.  212.  —  THE  LACRIMAL  APPARATUS. 
(Note  that  preference  is  given  to  the  spelling 
"lacrimal"  as  found  in  text,  instead  of  "lachry- 
mal" as  found  on  illustration.) 


446  ANATOMY  AND  PHYSIOLOGY       [CHAP.  XX 

It  is  often  considered  part  of  the  lacrimal  apparatus  as  it  secretes 
a  fluid  like  that  of  the  lacrimal  gland. 

Muscles  of  the  eye.  —  For  purposes  of  description  the  muscles 
of  the  eye  are  divided  into  two  groups :  (1)  intrinsic,  and  (2) 
extrinsic.  The  intrinsic  muscles  are  the  ciliary  muscle,  and  the 
muscles  of  the  iris.1  The  extrinsic  muscles  are  those  which  move 
the  eyeball  and  include  the  four  straight,  or  recti,  and  the  two 
oblique.  They  have  been  described  in  Chapter  VII. 

Nerves  of  the  eye.  —  The  nerves  which  are  supplied  to  the 
eye  are :  (1)  the  optic  nerve,  concerned  with  vision  only ;  (2)  the 
motor  oculi  nerve  which  controls  the  internal  rectus,  the  superior 
rectus,  the  inferior  rectus,  and  the  inferior  oblique  muscles ;  (3)  the 
pathetic  nerve  which  controls  the  superior  oblique  muscle ;  (4)  the 
abducens  which  controls  the  external  rectus ;  and  (5)  the  ophthal- 
mic, which  is  a  branch  of  the  trifacial  nerve,  supplies  general 
sensation. 

The  orbits.  —  The  orbits  are  the  bony  cavities  in  which  the 
eyeballs  are  contained. 

Seven  bones  assist  in  the  formation  of  each  orbit,  namely  frontal, 
malar,  maxilla,  palate,  ethmoid,  sphenoid,  and  lacrimal.  As  three 
of  these  bones  are  mesial  (frontal,  ethmoid,  and  sphenoid)  there 
are  only  eleven  bones  forming  both  orbits. 

The  orbit  is  shaped  like  a  four-sided  pyramid ;  the  apex,  directed 
backward  and  inward,  is  pierced  by  a  large  opening  —  the  optic 
foramen  —  through  which  the  optic  nerve  and  the  ophthalmic 
artery  pass  from  the  'cranial  cavity  to  the  eye.  A  larger  opening 
to  the  outer  side  of  the  optic  foramen  —  the  sphenoidal  fissure  — 
provides  a  passage  for  the  ophthalmic  vein  and  the  nerves  which 
carry  impulses  to  and  from  the  muscles,  i.e.,  the  motor  oculi, 
the  pathetic,  the  abducens,  and  the  ophthalmic.  The  base  of  the 
orbit,  directed  outward  and  forward,  forms  a  strong,  bony  edge 
for  protecting  the  eyeball  from  injury. 

Each  orbit  averages  about  2  inches  (5  cm.)  in  depth,  is  lined 
with  fibrous  tissue,  and  contains  a  pad  of  fat,  which  serves  as  a 
support  for  the  eyeball.  A  condition  of  emaciation  is  usually 
accompanied  by  sunken  eyes,  which  results  from  the  absorption 
of  this  fat,  and  the  consequent  sinking  of  the  eyeballs  in  the  orbits. 
Between  the  pad  of  fat  and  the  eyeball  is  a  serous  sac  —  the 

1  See  page  449. 


CHAP.  XX]     INTERNAL  AND   EXTERNAL  SENSES      447 

capsule  of  Tenon  —  which  envelops  the  eyeball  from  the  optic 
nerve  to  the  ciliary  region  and  forms  a  socket  in  which  the  eyeball 
rotates.  This  sac  secretes  a  lubricating  fluid,  the  function  of 
which  is  to  prevent  friction  when  the  eyeball  moves. 

The  eyeball.  —  The  eyeball  Is  spherical  in  shape,  but  its  trans- 
verse diameter  is  less  than  the  antero-posterior,  so  that  it  projects 


SUPERIOR  flECTUS 


CHOR010 


OPTIC  NERVE 


ORQIO 


• -INFERIOR  RTCTUS 

FIG.  213.  —  DIAGRAMMATIC  SECTION  OF  THE  EYE.     (Flint.) 

anteriorly,  and  looks  as  if  a  section  of  a  smaller  sphere  had  been 
engrafted  on  the  front  of  it. 

The  eyeball  is  composed  of  three  coats,  or  tunics,  and  contains 
three  refracting  media  or  humors.  They  are  as  follows :  — 

Tunics. — (1)  Protective:  (a)  sclera;      (6)  cornea. 

(2)  Vascular  :      (a)  choroid  ;  (6)  ciliary  body ;  (c)  iris. 

(3)  Visual :  retina. 
Refracting  media.  —  (1)  Aqueous. 

(2)  Crystalline  lens  and  capsule. 

(3)  Vitreous. 

Protective  tunics.  —  (a)  The  sclera,  or  white  of  the  eye,  covers 
the  posterior  five-sixths  of  the  eyeball.  It  is  composed  of  a  firm, 
unyielding,  fibrous  membrane,  thicker  behind  than  in  front, 
and  serves  to  protect  the  delicate  structures  contained  within  it, 
and  maintain  the  shape  of  the  eyeball.  It  is  opaque ;  white  and 


448  ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 

smooth  externally,  and  behind  is  pierced  by  the  optic  nerve.  In- 
ternally it  is  stained  brown  where  it  comes  in  contact  with  the 
choroid  coat.  It  is  supplied  with  very  few  blood-vessels,  and  the 
existence  of  nerves  in  it  is  doubtful. 

(6)  The  cornea  covers  the  anterior  sixth  of  the  eyeball.  It  is 
directly  continuous  with  the  sclera,  which,  however,  overlaps  it 
slightly  above  and  below,  as  a  watch  crystal  is  overlapped  by  the 
case  into  which  it  is  fitted.  The  cornea,  like  the  sclera,  is  composed 
of  fibrous  tissue,  which  is  firm  and  unyielding,  but,  unlike  the 
sclera,  it  has  no  color,  and  is  perfectly  transparent ;  it  has.  been 
aptly  termed  the  "  window  of  the  eye."  The  cornea  is  well  sup- 
plied with  nerves  and  lymph-spaces,  but  is  destitute  of  blood-ves- 
sels, so  that  it  is  dependent  on  the  lymph  contained  in  the  lymph- 
spaces  for  nutriment. 

Vascular  tunics.  —  (a)  The  choroid,  or  vascular  coat  of  the  eye, 
is  a  thin,  dark  brown  membrane  lining  the  inner  surface  of  the 
sclera.  It  is  composed  of  delicate  connective  tissue,  the  cells  of 
which  are  large  and  filled  with  pigment,  and  it  contains  a  close 
network  of  blood-vessels.  The  pigment  cells  and  blood-vessels 
render  this  membrane  dark  and  opaque,  so  that  it  darkens  the 
chamber  of  the  eye  by  preventing  the  reflection  of  light.  It  ex- 
tends to  within  a  short  distance  of  the  cornea. 

(6)  The  ciliary  body  is  located  between  the  choroid  and  the  iris, 
and  contains  the  ciliary  processes,  and  the  ciliary  muscle.  Just 
behind  the  edge  of  the  cornea,  the  choroid  is  folded  inward  and 
arranged  in  radiating  folds,  like  a  plaited  ruffle,  around  the  lens. 
There  are  about  seventy  of  these  folds,  and  they  constitute  the 
ciliary  processes.  They  are  well  supplied  with  nerves  and  blood- 
vessels, and  also  support  a  muscle,  the  ciliary  muscle.  The  fibres 
of  this  muscle  arise  from  the  sclera  near  the  cornea,  and  extending 
backward  are  inserted  into  the  outer  surface  of  the  ciliary  pro- 
cesses and  the  choroid.  The  action  of  this  muscle  determines  the 
position  of  the  lens. 

(c)  The  iris  (iris,  rainbow)  is  a  colored,  fibro-muscular  curtain 
hanging  in  front  of  the  lens  and  behind  the  cornea.  It  is  attached 
at  its  circumference  to  the  ciliary  processes,  with  which  it  is  prac- 
tically continuous,  and  is  also  connected  to  the  sclera  and  cornea 
at  the  point  where  they  join  one  another.  Except  for  this  attach- 
ment at  its  circumference,  it  hangs  free  in  the  interior  of  the  eye- 


CHAP.  XX]     INTERNAL   AND   EXTERNAL   SENSES      449 


ball.  In  the  middle  of  the  iris  is  a  circular  hole,  the  pupil,  through 
which  light  is  admitted  into  the  eye  chamber.  The  iris,  like  the 
choroid,  is  composed  of  connective  tissue  containing  a  large  num- 
ber of  pigment  cells  and  numerous  blood-vessels.  It  contains,  in 
addition,  two  sets  of  muscles. 
One  set  is  arranged  like  a 
sphincter  with  its  fibres  en- 
circling the  pupil,  and  is  called 
the  contractor  of  the  pupil. 
The  other  set  consists  of  fibres 
which  radiate  from  the  pupil 
to  the  outer  circumference  of 
the  iris,  and  is  called  the  di- 
lator of  the  pupil.  The  action 
of  these  muscles  is  antagonistic. 

The  posterior  surface  of  the 
iris  is  covered  by  a  thick  layer 
of  pigment  cells  designed  to 
darken  the  curtain  and  pre- 
vent the  entrance  of  Ught.  The 
anterior  surface  of  the  iris  is 
also  covered  with  pigment 
cells,  and  it  is  chiefly  these 
latter  which  cause  the  beautiful 
colors  seen  in  the  iris.  The 
different  colors  of  eyes,  how- 
ever, are  mainly  due  to  the 
amount,  and  not  to  the  color, 
of  the  pigment  deposited. 

Function  of  the  iris.  —  The  function  of  the  iris  is  to  regulate  the 
amount  of  light  entering  the  eye,  and  thus  assist  in  obtaining  clear 
images.  It  is  enabled  to  perform  this  function  by  the  action  of 
the  muscles  described  above,  as  their  contraction  or  relaxation 
determines  the  size  of  the  pupil.  When  the  eye  is  accommodated  1 
for  a  near  object,  or  stimulated  by  a  bright  light,  the  sphincter 
muscle  contracts  and  diminishes  the  size  of  the  pupil.  When, 
on  the  other  hand,  the  eye  is  accommodated  for  a  distant  object, 
or  the  light  is  dim,  the  dilator  muscle  contracts,  and  the  pupil  is 
pulled  wider  open. 

2  G  l  See  page  453. 


FIG.  214.  —  SEGMENT  OF  THE  IRIS, 
CILIARY  BODY,  AND  CHOROID.  Viewed 
from  the  internal  surface.  (Gerrish.) 


450 


ANATOMY  AND  PHYSIOLOGY      [CHAP.  XX 


Visual  tunic.  —  The  retina,  the  innermost  coat  of  the  eyeball, 
is  the  most  essential  part  of  the  organ  of  sight,  since  it  is  the  only 
one  directly  sensitive  to  light.  It  is  a  transparent  membrane  of 
a  grayish  color  that  is  formed  by  the  spreading  out  or  expansion 

of  the  optic  nerve.  It 
is  situated  between  the 
inner  surface  of  the  cho- 
roid  and  the  outer  sur- 
face of  the  vitreous 
humor,  and  extends 
from  the  entrance  of 
the  optic  nerve  forward 
to  the  margin  of  the 
pupil. 

The  retina  is  usually 
described  as  consisting 
of  eight  layers  and  two 
limiting  membranes ;  of 
these  layers,  three  are 
most  important :  — 

Eighth  layer,  or  layer 
of    nerve-fibres,   is   the 
internal  layer. 
Seventh  layer  is  the  layer  of  nerve-cells. 

First  layer,  or  layer  of  rods  and  cones,  is  the  external  layer. 
(See  Summary,  page  461.) 

The  fibres  of  the  optic  nerve,  after  piercing  the  sclera  and 
choroid  at  the  back  of  the  eye,  spread  out  and  form  the  eighth, 
or  innermost,  layer  of  the  retina.  The  fibres  then  pass,  with  more 
or  less  direct  communications,  peripherally  through  the  other 
layers,  until  they  may  be  said  to  terminate  in  the  layer  of  rods 
and  cones.  Rays  of  light  produce  no  effect  upon  the  optic  nerve 
without  the  intervention  of  the  rods  and  cones,  which  act  as  end 
organs. 

Blind  spot.  —  The  optic  nerve  pierces  the  eyeball  not  exactly 
at  its  most  posterior  point,  but  a  little  to  the  inner  side.  This 
point  where  the  optic  nerve  enters  is  called  the  blind  spot.  There 
are  no  rods  and  cones  at  this  spot,  and  rays  of  light  falling  upon 
it  produce  no  sensation. 


FIG.  215.  —  CHOROID  MEMBRANE  AND  IRIS 
EXPOSED  BY  THE  REMOVAL  OF  THE  SCLERA  AND 
CORNEA.  Twice  the  natural  size,  d,  one  of  the 
segments  of  the  sclera  thrown  back ;  I  and  k,  iris  ; 
c,  ciliary  nerves ;  e,  one  of  the  veins  of  the  choroid. 
The  ciliary  muscle  is  crossed  by  the  line  from  k,  and 
should  be  represented  as  radiating.  (Collins.) 


CHAP.  XX]     INTERNAL  AND  EXTERNAL  SENSES     451 


Macula  lutea.  —  There  is  one  point  of  the  retina  that  is  of  great 
importance,  and  that  is  the  macula  lutea,  or  yellow  spot.  It  is 
situated  about  one-twelfth  inch  (2.08  mm.)  to  the  outer  side  of  the 
exit  of  the  optic  nerve,  and  is  the  exact  centre  of  the  retina.  In 


LAYER  OF 
RODS  AND  CONES 


LAYER  OF 
NERVE-CELLS 


LAYER  OF 
NERVE-FIBRES 

FIG.  216.  —  DIAGRAMMATIC  SECTION  OF  THE  HUMAN  RETINA. 

its  centre  is  a  tiny  pit, — fovea  centralis, — which. is  the  centre 
of  direct  vision ;  that  is,  it  is  the  part  of  the  retina  which  is  al- 
ways turned  towards  the  object  looked  at.  From  this  point  the 
sensitiveness  of  the  retina  grows  less  and  less  in  all  directions. 
At  this  point  (fovea  centralis)  are  found  none  of  the  fibres  of  the 
optic  nerve,  but  a  great  increase  in  the  number  of  cones,  as  well  as 
in  their  size. 

Perception  of  light.  —  It  is  commonly  believed  that  all  space  is 
filled  by  ether,  a  medium  so  transparent  and  subtle  that  we  are 


452 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 


not  able  to  perceive  it  by  any  of  our  senses.     Transverse  vibrations 
or  waves  of  this  ether  produce  light,  which  enters  the  eye,  falls 

upon  the  retina,  and  acts  as  a 
stimulus.  It  is  supposed  that 
waves  of  light  cause  chemical 
changes  in  the  rods  and  cones 
which  give  rise  to  impulses  that 
are  carried  by  the  optic  nerve 
to  the  brain,  and  result  in  sight. 
Just  how  this  is  accomplished  is 
not  known,  but  the  rods  con- 
tain a  kind  of  pigment  which 
is  called  visual  purple,  and  this 
as  well  as  the  pigment  of  the 
retina  may  function  in  these 
changes. 

The  optic  chiasm.  —  The  fact 
that  the  two  retinae  and  the 
two  eyeballs  work  in  unison  is 
largely  due  to  the  crossing  of 
the  nerve-fibres  at  the  optic 
chiasm.  The  optic  nerve  from  each  eye  passes  backward  through 
the  optic  foramen,  and  shortly  after  leaving  the  orbit  the  two 
nerves  come  together,  and  the  fibres  from  the  inner  portion  of 
each  nerve  cross.  This  is  called  the  optic  chiasm,  and  is  really  an 
incomplete  crossing  of  fibres,  as  the  outer  fibres  do  not  cross. 
(See  Fig.  218.) 

Refracting  media.— 
(1)  The  aqueous  humor  is 
a  colorless,  transparent, 
watery  fluid,  which  fills 
the  aqueous  chamber;  the 
latter  is  the  space  bounded 
by  the  cornea  in  front  and 
by  the  lens,  suspensory  liga- 
ment, and  ciliary  body  be- 
hind. This  space  is  partially  divided  by  the  iris  into  an  anterior 
and  posterior  chamber. 

(2)  The  crystalline  lens  is  a  transparent,  refractive  body,  with 


FIG.  217.  — THE  POSTERIOR  HALF  OF 
THE  RETINA  OF  THE  LEFT  EYE  VIEWED 
FROM  BEFORE.  Twice  its  natural  s.ize. 
«,  cut  edge  of  the  sclera ;  ch,  choroid ; 
r,  retina ;  in  the  interior  at  the  middle, 
the  macula  lutea  with  the  depression  of 
the  fovea  centralis  is  represented  by  a 
slight  oval  shadow ;  toward  the  left  side 
the  light  spot  indicates  the  entrance  of 
the  optic  nerve  or  blind  spot.  (Collins.) 


Retina 


Optic  nerve 


Optic  chiasm 


Optic  tract 


FIG.  218.  —  DIAGRAM  OF  OPTIC  CHIASM. 


CHAP.  XX]     INTERNAL  AND   EXTERNAL  SENSES      453 

convex  anterior  and  posterior  surfaces  placed  directly  behind  the 
pupil,  where  it  is  retained  in  position  by  the  counterbalancing  pres- 
sure of  the  aqueous  humor  in  front,  and  the  vitreous  body  behind, 
and  by  its  own  suspensory  ligament  from  the  hyaloid  membrane. 
It  is  a  fibrous  body,  enclosed  in  an  elastic,  non-vascular  capsule. 
The  posterior  surface  is  considerably  more  curved  than  the  an- 
terior, and  the  curvature  of  each  varies  with  the  period  of  life.  In 
infancy,  the  lens  is  almost  spherical ;  in  the  adult,  of  medium  con- 
vexity ;  and  in  the  aged,  considerably  flattened.  Its  refractive 
power  is  much  greater  than  that  of  the  aqueous  or  vitreous  humor. 

(3)  The  vitreous  humor,  a  semi-fluid,  gelatinous  substance,  fills 
the  posterior  four-fifths  of  the  globe  of  the  eyeball.  It  is 
enclosed  in  a  thin  membrane  —  the  hyaloid  membrane.  This 
membrane  is  attached  to  the  retina  at  the  back  of  the  eyeball, 
and  furnishes  a  suspensory  ligament  to  the  lens.  Elsewhere  it  is 
perfectly  separable  from  its  surroundings.  The  vitreous  humor 
enclosed  in  this  capsule  distends  the  greater  part  of  the  sclera, 
supports  the  retina,  which  lies  upon  its  surface,  and  preserves  the 
spheroidal  shape  of  the  eyeball.  Its  refractive  power,  though 
slightly  greater  than  that  of  the  aqueous  humor,  does  not  differ 
much  from  that  of  water. 

Refraction.  —  Refraction  is  the  bending  or  deviation  in  the 
course  of  rays  of  light  in  passing  obliquely  from  one  transparent 
medium  into  another  of  different  density.  (See  page  505.) 

The  refractive  apparatus.  —  In  order  that  our  vision  of  objects 
looked  at  should  be  clear  and  distinct  it  is  necessary  that  the 
rays  of  light  entering  the  eye  should  be  focussed  on  the  retina. 
In  the  normal  eye  this  is  secured  by  the  mechanism  of  accommoda- 
tion (see  next  paragraph).  The  refractive  apparatus  consists  of 
the  aqueous  humor,  the  crystalline  lens,  and  the  vitreous  humor, 
which  have  just  been  described. 

Accommodation.  —  Accommodation  is  the  ability  of  the  eye 
to  adjust  itself  so  that  it  can  see  objects  at  varying  distances. 
The  theory  most  generally  accepted  is  that  the  ciliary  muscle  is 
the  active  agent  in  accommodation.  When  the  eye  is  at  rest  or 
fixed  upon  distant  objects  the  suspensory  ligament  exerts  a  tension 
upon  the  lens  which  keeps  it  flattened,  particularly  the  anterior 
surface  to  which  it  is  attached.  When  the  eye  becomes  fixed  on 
near  objects,  as  in  reading,  sewing,  etc.,  the  ciliary  muscle  contracts 


454 


ANATOMY  AND  PHYSIOLOGY      [CHAP.  XX 


and  draws  forward  the  choroid  coat,  which  in  turn  releases  the 
tension  of  the  suspensory  ligament  upon  the  lens,  and  allows  the 
anterior  surface  to  become  more  convex.  The  accommodation  for 
near  objects  is  an  active  condition  and  is  always  more  or  less 
fatiguing.  On  the  contrary,  the  accommodation  for  distant  ob- 

jects is  a  passive  condition,  in 
consequence  of  which  the  eye 
rests  for  an  indefinite  time  upon 
remote  objects  without  fatigue. 
Common  conditions  that  af- 
fect accommodation.  —  The  con- 
ditions that  affect  accommoda- 
tion are  :  (1)  hypermetropia, 
(2)  myopia,  (3)  presbyopia,  and 
(4)  astigmatism. 

Hypermetropia.  —  Hyper- 
metropia or  far-sightedness  is 
a  condition  in  which  rays  of 
light  from  near  objects  do  not 
converge  soon  enough  and  are 
brought  to  a  focus  behind  the 

retina.      This    IS    Usually    caused 

V  a  flattened  condition  of  the 
lens  or  cornea,  or  an  eyeball 

that  is  too  shallow,  and  convex  lenses1  are  used  to  concentrate 
and  focus  the  rays  more  quickly. 

Myopia.  —  Myopia  or  near-sightedness  is  a  condition  in  which 
rays  of  light  converge  too  soon,  and  are  brought  to  a  focus  before 
reaching  the  retina.  This  is  the  opposite  of  hypermetropia  and 
is  caused  by  a  cornea  or  lens  that  is  too  convex,  or  an  eyeball  of 
too  great  depth.  To  remedy  this  condition  concave  lenses  are 
worn  to  disperse  the  rays  and  prevent  their  being  focussed  too 
soon. 

Presbyopia.  —  Presbyopia  is  a  defective  condition  of  accom- 
modation in  which  distant  objects  are  seen  distinctly,  but  near 
objects  are  indistinct.  This  is  a  physiological  process  which  af- 
fects every  eye  sooner  or  later,  and  is  not  due  to  disease.  It  is 
said  to  be  caused  by  a  loss  of  the  elasticity  of  the  lens. 

page  501. 


FIG.  219.  —  DIAGRAM  ILLUSTRATING 
RAYS  or  LIGHT  CONVERGING  IN  (A)  A 


CHAP.  XX] 


SUMMARY 


455 


Astigmatism.  —  Astigmatism  is  the  condition  in  which  the  curva- 
ture of  the  cornea  or  lens  is  defective.  An  excess  of  curvature  in 
the  long  axis  of  the  cornea,  as  compared  with  that  of  its  horizontal 
axis,  is  the  more  common  defect.  Glasses  with  curvatures  the 
opposite  of  those  of  the  eyes  are  used  to  correct  this  defect. 

Inversion  of  images.  —  Due  to  refraction,  light  rays  as  they 
enter  the  eye  cross  each  other  and  cause  the  image  of  external 
objects  on  the  retina  to  be  inverted.  The  question  then  arises, 
"  Why  is  it  that  objects  do  not  appear  to  us  to  be  upside  down?  " 
This  question  is  easily  answered  if  we  remember  that  our  actual 
visual  sensations  take  place  in  the  brain,  and  that  the  projection 
of  these  sensations  to  the  exterior  is  a  secondary  act  that  has 
been  learned  from  experience. 


Sense-organ 


SUMMARY 

Peripheral  end  organ  or  receptor. 

Connecting  neurones  for  conduction  of  nerve-impulses. 
A  centre  in  the  nervous  system  for  interpretation  or  linkage 
with  motor  nerves. 


Sensation 


Perception  through  the  sense-organs. 
Interpreted  in  the  brain. 


Internal  or  those 
in  which  the 
sensations  are 
projected  to 
the  interior  of 
the  body.. 

Classification 


2.  External  or  those 
in  which  the 
sensations  are 
projected  to 
the  exterior  of 
body. 


Pain. 
Sensationsfromsemi- 

circular  canals  and 

vestibule    of    the 

internal  ear. 
Hunger. 
Thirst. 
Sexual  sense. 
Muscular  sense. 
Fatigue. 

Visceral  sensations. 
Pressure. 
Temperature     (heat 

and  cold). 
Taste. 
Smell. 
Hearing. 
Sight. 


456 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 


Cutaneous 
Sensations 


Pain 


Muscle 
Sense  . 


Hunger 


Thirst  . 


Taste   . 


Surface  of  skin  is  a  mosaic  of  sensory  spots  which  coincide 
with  location  of  special  end  organs  for  pressure,  cold, 
heat,  or  pain. 

1.  Fibres  for  light  pressure. 

2.  Fibres  for  small  difference 

of      temperature,     i.e., 
between  26°  and  37°  C. 
Special  characteristic  of  skin 


Classification 


Epicritic 


Protopathic 


area. 

1.  Fibres  for  pain. 

2.  Fibres  for  heat 

37°  C. 


above 


Sensibility  low,   localization 
poor. 


Much  evidence  to  support  the  theory  that  for  cutaneous 
pain  there  exists  a  special  set  of  fibres  with  a  specific 
energy  for  pain. 

Overstimulation  of  sensory  nerves  in  viscera  and  other 
parts  of  the  body  cause  pain. 

Pain  arising  in  viscera  and  referred  to  skin 
Referred  area  supplied  with  sensory  fibres  from 

Pain  the  same  spinal  segment  that  supplies 

organ  in  question. 

1.  End  organs  situated  in  tendons  and  between  fibres  of 
muscles. 

2.  Afferent  fibres  carry  impulses  to  centres  in  brain. 

3.  Efferent  fibres  carry  impulses  from  brain  to  muscle. 

Presumably  due  to  contractions  of  empty  stomach,  acting 
on  nerves  distributed  to  mucous  membrane. 

In  abnormal  conditions  contractions  may  be  weak  or  fail 
to  occur  at  all. 

I  Presumably  due  to  stimulation  of  nerves  of  pharynx  by 
\      low  water  content  in  tissues. 

1.  Taste-buds  are  end  organs. 

Sensory  ap-  2.  Nerve-fibres  of  trifacial,  facial,  and  glos- 
paratus  sopharyngeal  nerves. 

3.  Centre  in  brain. 

Solution  of  sapid  substances  must  come  in  contact  with 
taste-buds. 

Surface  of  tongue. 

Taste-buds  are  distributed  over    Soft  palate  and  fauces. 

Tonsils  and  pharynx. 


CHAP.  XX] 


SUMMARY 


457 


Tongue     . 


Smell   . 


Hearing 


Freely  movable  muscular  organ. 

Attached  to  hyoid  bone,  epiglottis,  and  pillars  of  the  fauces. 

Circumvallate. 


Surface  covered  by  papillae 


Nerves 


Sense  of 


Sensory 


Fungiform. 


Filiform. 

Lingual,  branch  of  trifacial. 

Chorda  tympani,   branch  of 
the  facial. 

Glossopharyngeal. 
Motor  —  Hypoglossal. 
1.  Taste 


2.  Temperature 

3.  Pressure 

4.  Pain 


Are  all  well  developed. 


f  Olfactory  nerve-endings. 
Sensory  ap-    |  Olfactory  nerve-fibres. 

paratus        [  Centre  in  brain  —  olfactory  bulb. 

f  Minute  particles  of  f  Must     be     capable 
Odors  solid  matter  of      solution      in 

[  Gases  [     mucus. 

Olfactory  nerve-endings  found  in  lining  of  upper  part  of 

nose  (smell). 

Branches  of  trigeminal  nerve  found  in  lining  of  lower  part 
of  nose  (pressure) . 


Auditory  ap- 
paratus 


External  ear. 

Middle  ear. 

Internal  ear. 

Auditory  nerve. 

Centre  in  brain. 
Air-waves  enter  external  auditory  canal  and  cause  vibra- 
tions of  drum-membrane.     The  vibrations  are  conveyed 
to  nerve-endings  of  organ  of  Corti,  and  thence  by  the 
auditory  nerve  to  the  brain. 


External  Ear 


Pinna,  or 
auricle 


Auditory 
canal 


Structure  —  Cartilaginous  framework, 

some    fatty    and    muscular    tissue, 

covered  with  skin. 
Function  —  Collects  sound-waves  and 

reflects  them  into  the  auditory  canal. 
1  in.  long,  partly  cartilage,  partly  bone. 
Closed  internally  by  the  f  Membrana 

drum-membrane  1      tympani. 

Hairs  directed  outward. 
Ceruminous  glands  secrete  a  yellow, 

pasty  substance. 


458 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 


Middle  Ear 


Bones 


Openings 


Bony 

Labyrinth 


An  irregular  cavity  in  the  temporal  bone. 
Five  or  six  drops  of  water  will  fill  it. 
Malleus  (hammer). 
Incus  (anvil). 
Stapes  (stirrup). 

Fenestra  ovalis  —  closed  by  a  mem- 
brane and  the  stapes. 
Fenestra  rotunda  —  closed  by  a  mem- 
brane. 
Eustachian  tube  —  connects  with  the 

pharynx ;  ventilates  cavity. 
Vestibule  —  antechamber   just   inside 

of  fenestra  ovalis. 
Semicircular  f  Three  in  number. 

canals        1  Open  into  vestibule. 
Vestibular  branch  ~f  auditory  nerve 
distributed  to  vestibule  and  semi- 
circular canals. 

A  spiral  tube. 
2 1  turns  around  modiolus. 
Cochlea   \  Fenestra  rotunda. 

Cochlear  branch  of  the  au- 
ditory nerve. 

Surrounded  by  perilymph. 
Internal  Ear  Contains  endolymph. 

, .,    ,    f  Saccule. 
Lines  the  vestibule  1  TTJ  .  , 
I  Utricle. 

Lines  the  semicircular  canals. 

Membranous     Lines  the  cochlea,  and  here  it  is  called 
Labyrinth  the  canalis  cochlearis,  or  scala  media. 

Membrana  basilaris  is  name  given  to 

membrane  at  base  of  canal. 
Organ  of   Corti,  name   given  to   end 
organs  of  auditory  nerve  lodged  on 
membrana  basilaris. 
Cochlear  —  terminates  in  and  around 
Auditory  the  cells  of  organ  of  Corti. 

Nerve  Vestibular  —  terminates    in    hair-cells 

of  saccule,  utricle,  and  ampulla. 
Function  of  the  vestibule  and  semicircular  canals. 
Lining  membrane  supplied  with  sensory  hairs  which  connect 

with  vestibular  nerve. 

Contains  several  small  otoliths  which  float  in  the  endolymph. 
Flowing  of  the  endolymph  stimulates  the  sensory  hairs; 
this  is  transmitted  to  the  vestibular  nerve,  thence  to 
auditory  nerve,  thence  to  brain. 


Sense  of 
Equilibrium 


CHAP.  XX] 


SUMMARY 


459 


Visual  Ap- 
paratus 


Accessory 
Organs 


Accessory 
organs 


Eyebrows 


Eyelids 


Eye. 

Optic  nerve. 

Centre  in  brain. 

Eyebrows. 
Eyelids. 

Lacrimal  apparatus. 
Muscles. 
f  Thickened    ridges   of    skin   furnished    with 

short,  thick  hairs. 
Control  to  a  limited  extent  amount  of  light 

admitted  to  eye. 
Folds  of  connective  tissue  covered  with  skin, 

lined  with  mucous  membrane  (conjunctiva), 

which  is  also  reflected  over  the  eyeball. 
Provided  with  lashes. 

Closed  by  orbicularis  palpebrarum  muscle. 
Upper    lid    raised    by    levator     palpebrae 

superioris. 

Slit  between  lids  called  palpebral  fissure. 
Inner  angle  of  slit  called  internal  canthus. 
Outer  angle  of  slit  called  external  canthus. 
Function  is  protection.     Serve  as  shades. 
Tarsal  glands  are  a  row  of  glands  embedded  in 

tarsal  cartilage  of  each  lid. 
Lacrimal  gland  —  in  the  upper  and  outer  part 

of  the  orbit.     Secretes  tears. 
Ducts  —  7  to  12  lead  from  gland  to  con- 
junctiva. 
Canaliculi  —  2  canals  i  to  t  in.  long,  begin 

at  punctse  and  open  into  lacrimal  sac. 
Lacrimal  sac  —  upper  dilated  portion  of  the 

nasal  duct. 
Nasal  duct  —  canal  f  in.  long,  extends  from 

lacrimal  sac  to  the  nose. 

Secretion  constant. 
Moisten  the  eyeball  and  help  to 
moisten  inspired  air. 

_      .     f  Water. 
Consist  |  SalL 

I  Albumin. 

Carried  off  by  nasal  duct. 
Superior  rectus. 
Inferior  rectus. 
Internal  rectus. 
External  rectus. 
Superior  oblique. 
Inferior  oblique. 
Ciliary     /  Determines    the  posi- 

muscle  \     tion  of  the  lens. 
Muscles   /  Contractor  of  pupil. 

of  iris  \  Dilator  of  pupil. 


Lacrimal 
apparatus 


Muscles 


Tears 


Extrinsic 


Intrinsic 


460 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 


1.  Optic  nerve 

Nerves  of 
Eye     .     . 

2.  Motor 
oculi 
controls 

Internal  rectus  muscle. 
Superior  rectus  muscle. 
Inferior  rectus  muscle. 
Inferior  oblique  muscle. 

3.  Pathetic  controls  the  superior  oblique  muscle. 

4.  Abducens  controls  the  external  rectus  muscle. 

5.  Ophthalmic. 


Orbit . 


Bony  cavity  formed  by  seven  bones 


Frontal. 

Malar. 

Maxilla. 

Palate. 

Ethmoid. 

Sphenoid. 

Lacrimal. 
Lined  by  fibrous  tissue. 
Contains  pad  of  fat  —  supports  eyeball. 
Capsule  of  Tenon  —  prevents  friction  when  eyeball  moves. 
Shaped  like  four-sided  pyra-  j  Apex  directed  backward. 

mid  I  Base  directed  forward. 

Optic  foramen  —  opening  for  passage  of  optic  nerve  and 

ophthalmic  artery. 

Sphenoidal  fissure  —  opening  for  passage  of  ophthalmic 
vein  and  motor  oculi,  pathetic  and  abducens  nerves. 


Eyeball 


Spherical  in  shape,  but  it  projects  anteriorly. 

1.  Protective  —  sclera  and  cornea. 
Tunics     .      •!  2.  Vascular  —  choroid,  ciliary  body  and  iris. 

3.  Visual  —  retina. 

1.  Aqueous. 
Media      .      \  2.  Crystalline  lens  and  capsule. 

3.  Vitreous. 


Protective 
Tunics 


Sclera 


Cornea 


Tough,  fibrous,  opaque. 

Covers  posterior  |  of  eyeball. 

Stained  brown  internally. 

Fibrous,    transparent  —  covers   anterior    of 

eyeball. 
Well  supplied  with  nerves. 


CHAP.  XX] 


SUMMARY 


461 


Vascular 
Tunics 


Choroid 


Ciliary  Body 


Iris 


Vascular  coat,  lines  the  sclera. 

Composed  of  connective  tissue  cells  filled  with 
pigment. 

Terminates  in  front  by  the  ciliary  processes. 

Ciliary  processes  70  to  80  parallel  folds  of  the 
choroid,  rising  gradually  from  behind  and 
forming  a  plaited  zone  between  the  choroid 
and  iris. 

Support  ciliary  muscle  —  action  of  this 
muscle  determines  the  position  of  the  lens. 

A  circular  curtain.  Central  perforation  — 
pupil. 

Pupil  contracted  by  circular  muscle-fibres. 

Pupil  dilated  by  radial  muscle-fibres. 

Contains  pigment  —  amount  of  which  deter- 
mines color  of  the  eyes. 

Hangs  free  except  for  attachment  at  circum- 
ference to  the  ciliary  processes  and  choroid. 

Function  —  Regulates  amount  of  light  enter- 
ing eye. 


Visual 
Tunic 
or 
Retina 


Visual  layer  —  transparent  membrane  of  nervous  and  con- 
nective tissue  situated  between  the  choroid  and  vitreous 
humor.  Formed  by  the  spreading  out  of  optic  nerve. 

Has  eight  layers  and  two  membranes.  Counting  from  the 
choroid  inward  as  follows  :  — 

Pigment  layer,  usually  described  as  a  membrane. 

1.  Layer  of  rods  and  cones  (perceptive  layer)  —  external 

layer. 

2.  Limitans  externa. 

3.  External  granules. 

4.  External  molecular. 

5.  Internal  granules. 

6.  Internal  molecular. 

7.  Ganglion  or  nerve-cells. 

8.  Optic  nerve-fibres  —  innermost  layer. 
Membrana  limitans  interna. 

Entrance  of  optic  nerve. 
There  are  no  rods  and  cones. 
Totally  insensitive  to  light. 
TV  in.  outside  the  blind  spot. 
Central  pit  —  fovea  centralis  —  is  the  centre  of 
[      direct  vision. 
Vibrations  of  ether  enter  eye,  strike  on  rods  and   cones, 
thence  sensation  is  carried  to  the  visual  centre  in  the  brain. 


Blind 
Spot 

Macula 
Lutea 


462 


ANATOMY  AND   PHYSIOLOGY      [CHAP.  XX 


Refractive 
Apparatus 


Aqueous 


Crystal- 
line 
lens 


Vitreous 


Aqueous  chamber  is  between  cornea  in  front,  and 
lens,  suspensory  ligament,  and  ciliary  body 
behind.  Aqueous  humor  is  a  colorless,  trans- 
parent, watery  fluid. 

Fibrous  body  enclosed  in  an  elastic  capsule. 

Double  convex  in  shape.  Situated  behind  the 
pupil. 

Held  in  position  by  counterbalancing  of  the 
aqueous  and  vitreous  humors  and  the  sus- 
pensory ligament. 

Semi-fluid,  gelatinous  substance. 

Fills  the  posterior  four-fifths  of  the  globe  of 
the  eyeball,  and  is  enclosed  in  the  hyaloid 
membrane.  Distends  the  sclera  and  supports 
the  retina. 


Refraction  —  Bending  or  deviation  in  the  course  of  rays  of  light,  in  pass- 
ing obliquely  from  one  transparent  medium  into  another 
of  different  density. 

Accommodation  —  Ability  of  the  eye  to  adjust  itself  so  that  it  can  see 
objects  at  varying  distances. 

f  Far-sightedness. 

Cause  —  Rays  of  light  do  not  converge 
soon  enough. 

Near-sightedness . 

Cause  —  Rays  of  light  converge  too  soon. 

Defective  condition  of  accommodation 
in  which  distant  objects  are  seen  dis- 
tinctly, but  near  objects  are  indistinct. 

Condition  in  which  the  curvature  of  the 
cornea  or  lens  is  defective. 


Hypermetropia 

Conditions 
that  affect 

Myopia   .     . 

Accommo- 

dation 

Presbyopia  . 

Astigmatism 

CHAPTER  XXI 

THE  ORGANS  OF  GENERATION:  PHYSIOLOGY  OF 
REPRODUCTION 

Female  generative  organs.  —  The  female  generative  organs 
are  divided  into  an  internal  and  an  external  group.  The  internal 
are  contained  within  the  true  pelvis,  and  the  external  are  grouped 
under  the  name  of  vulva  or  pudendum. 

INTERNAL  GENERATIVE  ORGANS 

The  internal  generative  organs  comprise  the  following  struc- 
tures :  — 

(1)  Ovaries,  two  glandular  organs  in  which  the  ova  are  formed. 

(2)  Fallopian  [uterine]    tubes,  two  canals  through  which  the 
ova  reach  the  uterine  cavity. 

(3)  Uterus,  a  hollow,  pear-shaped  organ,  which  receives  the 
ovum. 


VAGINA 


FIG.  220.  —  UTERUS,  OVARIES,  AND  FALLOPIAN  TUBES. 


(4)  Vagina,  a  canal  extending  from  the  uterus  to  the  vulva. 
Ovaries.  —  The    ovaries    are    two    almond-shaped,    glandular 
bodies,  situated  one  on  each  side  of  the  uterus,  in  the  posterior  fold 

463 


464  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 

of  the  broad  ligament,  behind  and  below  the  Fallopian  tubes. 
Each  ovary  is  attached  at  its  inner  end  to  the  uterus  by  a  short 
ligament,  —  the  ligament  of  the  ovary,  —  and  at  its  outer  end  to 
the  Fallopian  tube  by  one  of  the  fringe-like  processes  of  the  fim- 
briated  extremity.  The  ovaries  each  measure  about  one  and  a 
half  inches  (3.8  cm.)  in  length,  three-fourths  of  an  inch  (1.9  cm.) 
in  width,  and  one-third  of  an  inch  (8.5  mm.)  in  thickness,  and  weigh 
from  one  to  two  drachms  (3.7  to  7.5  gms.). 

Function.  —  The  function  of  the  ovaries  is  to  produce,  develop 
and  mature  the  ova,  and  to  discharge  them  when  fully  formed. 
In  addition,  the  ovary  furnishes  an  internal  secretion,  which  is 
picked  up  by  the  blood. 

Structure.  —  If  the  substance  of  an  ovary  be  minutely  examined 
it  is  found  to  consist  of :  (1)  a  stroma  or  bed  composed  of  white 
and  yellow  fibrous  tissue,  blood-vessels,  lymphatics,  and  nerves, 
(2)  Graafian  follicles,  and  (3)  a  covering  of  columnar  epithelial  cells, 
called  germinal  epithelium,  which  is  continuous  with  the  peritoneum. 

Graafian  (vesicular)  follicles.  —  The  Graafian  follicles  are  sacs 
or  vesicles  which  contain  the  ova  and  are  embedded  in  the  meshes 
of  the  stroma. 

Each  follicle  consists  of :  (1)  an  outer  coat  of  fibrous  tissue  that 
is  derived  from  the  stroma,  and  connected  with  it  by  a  plexus  of 
blood-vessels,  and  (2)  an  inner  layer  of  nucleated  cells.  With 
the  exception  of  the  smallest  vesicles  each  one  is  filled  with  fluid, 
and  suspended  in  this  fluid  is  an  ovum  surrounded  by  a  mass  of 
cells,  called  the  discus  proligerus. 

At  birth  the  ovaries  are  said  to  contain  about  36,000  vesicles, 
each  measuring  from  ^-g-  to  y^y  of  an  inch  in  diameter,  but  only  a 
small  number  of  these  ever  develop,  as  the  great  majority  shrink 
and  disappear.  At  the  time  of  puberty  the  ovaries  enlarge,  be- 
come very  vascular,  and  some  of  the  follicles  increase  in  size.  As 
the  follicles  increase  in  size  they  approach  the  surface  and  begin 
to  form  small  protuberances  on  the  outside  of  the  ovary.  When 
fully  matured  the  wall  of  the  ovary  and  the  wall  of  the  follicle 
burst  at  the  same  point,  and  the  contents  of  the  follicle  —  the 
fluid,  the  ovum,  and  the  surrounding  cells  —  escape.  This  pro- 
cess of  development,  maturation,  and  rupture  of  a  follicle  is  known 
as  ovulation,  and  continues  at  regular  intervals  from  puberty  to 
the  menopause. 


CHAP.  XXI]    THE   ORGANS   OF   GENERATION  465 

The  corpus  luteum.  —  After  the  rupture  of  a  follicle,  and  the 
escape  of  the  ovum,  the  walls  collapse  and  the  cavity  becomes 
filled  with  blood  which  forms  a  clot.  Later  this  clot  becomes 
surrounded  by  cells  containing  a  yellow  pigment,  which  gives  the 
follicle  a  yellow  color,  and  hence  it  is  known  as  the  corpus  luteum. 
The  size  and  duration  of  the  corpus  luteum  is  dependent  on 
whether  pregnancy  occurs  or  not.  If  pregnancy  does  not  occur  the 
corpus  luteum  increases  in  size  for  two  or  three  weeks  and  then  is 
absorbed.  If  pregnancy  does  occur  the  corpus  luteum  increases 
in  size  during  the  first  few  months,  and  does  not  show  retrogressive 
changes  until  about  the  sixth  month.  Opinions  differ  regarding 
the  physiological  importance  of  the  corpus  luteum.  Some  physi- 
ologists regard  it  as  a  protective  mechanism  by  means  of  which  the 
cavity  resulting  from  the  rupture  of  the  follicle  is  filled  with  a 
tissue  which  can  be  easily  absorbed.  Others  attribute  to  the  cor- 
pus luteum  secretory  functions  of  the  most  important  character 
in  connection  with  menstruation,  the  implantation  of  the  fertilized 
ovum  and  its  subsequent  growth. 

Fallopian  tubes.  —  The  Fallopian  tubes  or  oviducts  are  two  in 
number,  one  on  each  side,  and  pass  from  the  upper  angles  of  the 
uterus  in  a  somewhat  tortuous  course  between  the  folds  and  along 
the  upper  margin  of  the  broad  ligament,  towards  the  sides  of  the 
pelvis.  They  are  about  four  inches  (10  cm.)  long,  and  at  the  point 
of  attachment  to  the  uterus  are  very  narrow,  but  gradually  in- 
crease in  size  so  that  the  distal  end  is  larger.  The  margin  of  the 
distal  end  is  surrounded  by  a  number  of  fringe-like  processes  called 
fimbrice.  One  of  these  fimbrise  is  attached  to  the  ovary.  The 
uterine  opening  of  the  tube  is  minute,  and  will  only  admit  a  fine 
bristle ;  the  abdominal  opening  is  comparatively  much  larger. 

The  Fallopian  tube  consists  of  three  coats :  — 

(1)  The  external,  or  serous,  coat  is  derived  from  the  peritoneum. 

(2)  The  middle,  or  muscular,  coat  has  two  layers :   one  a  layer 
of  longitudinal  cells  and  the  other  of  circular  cells. 

(3)  The  internal,  or  mucous*  coat  is  arranged  in  longitudinal 
folds  and  covered  with  ciliated  epithelium.     It  is  continuous  at 
the  inner  end  with  the  mucous  lining  of  the  uterus,  and  at  the  dis- 
tal end  with  the  serous  lining  of  the  abdominal  cavity.     This  is 
the  only  place  in  the  body  where  a  mucous  and  serous  lining  are 
continuous  with  one  another. 

2n 


466  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 

Function.  —  The  function  of  the  Fallopian  tubes  is  to  convey 
the  ova  from  the  ovaries  to  the  uterus.  Just  how  the  ovum, 
after  its  discharge  into  the  abdominal  cavity,  reaches  the  Fallopian 
tube  is  not  known.  It  is  thought  that  the  movement  of  the  cilia 
on  the  fimbrise  and  in  the  tubes  produces  a  current  which  draws  the 
ovum  into  the  tube.  After  the  ovum  enters  the  tube  it  is  carried 
to  the  uterus  by  the  peristaltic  action  of  the  tube  and  the  move- 
ment of  the  cilia.  It  is  considered  probable  that  many  of  the  ova 
discharged  from  the  ovaries  remain  in  the  abdominal  cavity, 
because  of  failure  to  reach  the  tubes.  These  ova  disintegrate,  are 
absorbed,  and  carried  away  by  the  blood.  Occasionally  such  an 
ovum  becomes  impregnated  and  ectopic  gestation  results. 

The  uterus.  —  The  uterus  is  a  hollow,  pear-shaped  organ.  In 
the  virgin  state  it  is  situated  in  the  pelvic  cavity  between  the  blad- 
der and  the  rectum.  Its  length  is  estimated  to  be  about  three 
inches  (7.5  cm.),  its  width  two  inches  (5  cm.)  at  the  upper  part, 
and  its  thickness  one  inch  (2.5  cm.).  During  pregnancy  the  uterus 
becomes  enormously  enlarged,  attains  the  length  of  a  foot  (30 
cm.)  or  more,  extends  into  the  umbilical  region,  and  measures 
about  eight  to  ten  inches  (20  to  25  cm.)  in  width.  After  partu- 
rition the  uterus  returns  to  almost  its  original  size,  but  is  al- 
ways larger  than  before  pregnancy.  After  the  menopause,  the 
uterus  becomes  smaller  and  atrophies. 

Divisions.  —  For  purposes  of  description  the  uterus  is  divided 
into  three  parts :  the  fundus,  body,  and  neck. 

The  fundus  is  the  convex  part  above  the  entrance  of  the  tubes. 

The  body  is  the  part  between  the  fundus  and"  the  neck. 

The  cervix  or  neck  is  the  lower  constricted  part  and  extends 
from  the  body  of  the  uterus  into  the  vagina. 

The  cavity  of  the  uterus  is  small  because  of  the  great  thickness 
of  its  walls;  that  part  within  the  body  is  triangular  in  shape 
(v),  and  has  three  openings,  one  at  each  upper  angle,  communi- 
cating with  the  Fallopian  tubes,  and  one,  the  internal  orifice,  open- 
ing into  the  cavity  of  the  cervix  below.  The  cavity  of  the  cervix, 
which  is,  of  .course,  continuous  with  the  cavity  in  the  body,  is 
constricted  above,  where  it  opens  into  the  body  by  means  of  the 
internal  orifice  (internal  os),  and  below,  where  it  opens  into  the 
vagina  by  means  of  the  external  orifice  (external  os).  Between 
these  two  openings  the  canal  of  the  cervix  is  somewhat  enlarged. 


CHAP.  XXI]    THE   ORGANS   OF   GENERATION  467 

Structure.  —  The  walls  of  the  uterus  are  thick  and  consist  of 
three  coats :  — 

(1)  An  external  serous  coat  derived  from  the  peritoneum.     It 
covers  all  of  the  uterus,  and  the  posterior  surface  of  the  cervix, 
but  not  the  anterior  surface. 

(2)  A   middle  muscular  coat   which   forms  the   bulk  of  the 
uterine   walls.     It    consists  of  layers   of   plain   muscular   tissue 
intermixed    with    blood-vessels,    lymphatics,    and    nerves.     The 
arrangement  of  the  muscles  is  very  complex,  as  they  run  cir- 
cularly, longitudinally,  spirally,  and  cross  and  interlace  in  every 
direction. 

(3)  An  internal  mucous  membrane,  which  is  continuous  with 
that  lining  the  vagina  and  Fallopian  tubes.     It  is  highly  vascular, 
provided  with  numerous  mucous  glands,  and  is  covered  with  cili- 
ated epithelium. 

Blood  supply  of  uterus.  —  The  uterus  is  abundantly  supplied 
with  blood-vessels.  The  blood  reaches  the  uterus  by  means  of 
the  uterine  arteries  from  the  internal  iliacs,  and  the  ovarian  ar- 
teries from  the  aorta.  Where  the  neck  joins  the  body  of  the 
uterus,  the  arteries  from  both  sides  are  united  by  a  branch  vessel, 
called  the  circumflex  artery.  If  this  branch  is  cut  during  a  surgi- 
cal operation,  or  a  tear  of  the  neck  during  parturition  extends  so 
far  as  to  sever  it,  the  hemorrhage  is  very  profuse.  The  arteries 
are  remarkable  for  their  tortuous  course  and  frequent  anastomoses. 
The  veins  are  of  large  size,  and  correspond  in  their  behavior  to  the 
arteries. 

Position  of  the  uterus.  —  The  uterus  is  not  firmly  attached  or  ad- 
herent to  any  part  of  the  skeleton.  It  is,  as  it  were,  suspended  in 
the  pelvic  cavity  by  ligaments.  A  full  bladder  pushes  it  back- 
ward ;  a  distended  rectum,  forward.  It  alters  its  position,  by 
gravity,  or  with  change  of  posture.  During  gestation  it  rises  into 
the  abdominal  cavity. 

The  fundus  of  the  uterus  is  inclined  forward,  and  the  external 
orifice  is  directed  downward  and  backward.  (See  Fig.  221.) 
Anteversion  is  the  condition  where  the  fundus  turns  too  far  forward. 
Retroversion  is  the  condition  where  the  fundus  inclines  backward. 
A  bend  may  exist  where  the  neck  joins  the  body,  and  if  the  body 
is  bent  forward,  it  is  described  as  anteflexion;  if  bent  backward, 
retroflexion. 


468 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XXI 


Ligaments.  —  The  uterus  is  suspended  by  five  ligaments. 
Three  are  arranged  in  pairs. 

1.  The  broad,  or  lateral  ligaments,  two  in  number,  are  folds 
of  peritoneum  slung  over  the  front  and  back  of  the  uterus,  and 
extending  laterally  to  the  walls  of  the  pelvis.  They  are  composed 
of  two  opposed,  serous  layers,  and  between  these  layers  are  found 
the  following  structures:  (a)  Fallopian  tubes;  (6)  the  ovaries 


FIG.  221. — INTERNAL  ORGANS  OF  GENERATION.     (Cooke.) 

and  their  ligaments;  (c)  the  round  ligaments;  (d)  blood-vessels 
and  lymphatics ;  (e)  nerves ;  (/)  some  smooth  muscle  tissue. 

The  posterior  fold  covers  the  back  of  the  uterus,  and  extends 
far  enough  below  to  also  cover  the  upper  one-fifth  of  the  back  wall 
of  the  vagina,  when  it  turns  up  and  is  reflected  over  the  anterior 
wall  of  the  rectum.  Thus  the  uterus,  with  and  between  its  two 
broad  ligaments,  forms  a  transverse  partition  in  the  pelvic  cavity, 
the  bladder,  vagina,  and  urethra  being  in  the  front  compartment, 
and  the  rectum  in  the  back  compartment. 

The  smooth  muscles  of  the  broad  ligaments  are  derived  from  the 


CHAP.  XXI]    THE  ORGANS  OF  GENERATION  469 

superficial  muscular  layer  of  the  uterus.     They  pass  out  between 
the  serous  folds  and  become  attached  to  the  pelvic  fascia. 

2.  The  round  ligaments  are  two  rounded,  fibro-muscular  cords, 
situated  between  the  folds  of  the  broad  ligament.     They  are  about 
four  and  a  half  inches  (11.3  cm.)  long,  and  take  their  origin  from 
the  upper  angle  of  the  uterus  (on  either  side),  in  front  and  a  little 
below  the  attachment  of  the  Fallopian  tube.    They  extend  for- 
ward and  outward,  and  finally  end  in  the  tissues  of  the  labia  majora 
and  mons  Veneris.    The  round  ligaments  are  composed  of  muscles, 
areolar  tissue,  blood-vessels,  and  nerves. 

3.  The  utero-sacral  ligaments  extend  between  the  cervix  and 
sides  of  the  rectum.     They  serve  to  connect  the  cervix  and  vagina 
with  the  sacrum,  and  are  partly  serous,  partly  of  smooth  muscular 
tissue. 

4.  Between  the  bladder  and  uterus  the  peritoneum  forms  a 
shallow  pouch  called  the  utero-vesical  pouch.     This  peritoneum, 
which  forms  the  floor  of  the  pouch,  is  described  as  the  anterior 
ligament  of  the  uterus. 

5.  Behind  the  uterus  the  peritoneum  forms  a  second  and  deeper 
pouch  called  the  recto-vaginal,  or  cul-de-sac,  of  Douglas.    This 
peritoneum  is  described  as  the  recto-vaginal  ligament. 

Function.  —  The  function  of  the  uterus  is  to  receive  the  ovum 
from  the  Fallopian  tubes,  and  if  it  becomes  fertilized  to  retain  it 
during  its  development.  Later  when  the  ovum  has  developed 
into  a  mature  foetus,  it  is  expelled  from  the  uterus,  chiefly  by  the 
contractions  of  the  uterine  walls. 

The  vagina.  —  The  vagina  is  a  musculo-membranous  canal 
which  encircles  the  lower  portion  of  the  cervix,  and  extends 
downward  and  forward  from  the  uterus  to  the  vulva. 

The  posterior  wall  is  about  three  and  a  half  inches  (8.75  cm.) 
long,  while  the  anterior  wall  is  only  two  and  one-half  inches  (6.25 
cm.).  The  front,  or  anterior  wall,  is  united  by  connective  tissue 
with  the  posterior  walls  of  the  bladder  and  urethra,  the  partition, 
or  septum,  between  the  bladder  and  vagina  being  called  the 
vesico-vaginal,  and  that  between  the  urethra  and  vagina  the 
urethro-vaginal,  septum. 

Structure.  —  The  vagina  is  made  up  of  three  coats :  an  outer, 
fibrous;  middle,  muscular;  and  inner,  mucous,  which  in  the 
ordinary  contracted  state  is  thrown  into  folds,  its  anterior  and 


470  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XXI 

posterior  walls  being  in  contact.  The  muscular  coat  increases 
during  pregnancy,  and  the  mucous  coat,  because  of  the  transverse 
folds,  or  rugae,  allow  of  dilatation  of  the  canal  during  labor  and 
birth. 


DORSAL  VC 
OF   CLITORIS 


f>ncpucc  or 

CLITORIS 

CLANS   CLI- 

TORIOIS 


FIG.  222.  —  SAGITTAL  SECTION  OF  THE  VAGINA  AND  NEIGHBORING  PARTS. 

(Gerrish.) 

THE  EXTERNAL  ORGANS 

The  external  organs  of  generation  are  grouped  under  the 
name  of  vulva  or  pudendum  and  include  the  following :  — 

1.  Mons  Veneris  4.  The  Clitoris 

2.  Labia  Majora  5.  The  Hymen 

3.  Labia  Minora  „    ^,      ,     f  Vulvo- vaginal 

6.  Glands  {  TT 

[  Urethral 

Mons  Veneris.  —  The  mons  Veneris  is  an  eminence  situated  in 
front  of  the  pubic  bones.  It  consists  of  areolar,  adipose,  and 
fibrous  tissue  covered  with  skin  and  after  puberty  with  hair. 

Labia  majora.  —  The  labia  majora  are  two  longitudinal  folds 
of  skin  containing  adipose  and  connective  tissue.  They  are  con- 
tinuous with  the  mons  Veneris  in  front,  and  extend  to  within  an 
inch  (25  mm.)  of  the  anus  behind. 

Labia  minora.  —  The  labia  minora  are  two  longitudinal  folds 
of  modified  epithelium  situated  between  the  labia  majora.  They 
are  joined  anteriorly  in  the  hood  or  prepuce  of  the  clitoris,  and 
extend  downward  and  backward  for  about  one  and  one-half  inches 
(3.8  cm.). 


CHAP.  XXI]    THE  ORGANS   OF  GENERATION 


471 


The  clitoris.  —  The  clitoris  is  a  small  body  situated  at  the  apex 
of  the  triangle  formed  by  the  junction  of  the  labia  minora.  It 
contains  many  vessels  and  nerves  and  is  almost  completely  cov- 
ered by  the  hood  or 
prepuce. 

The  hymen.  —  The 
hymen  is  a  fold  of 
mucous  membrane 
which  surrounds  the 
lower  part  of  the  va- 
gina and  renders  the 
orifice  smaller.  It  is 
quite  elastic  and  may 
remain  intact  even 
after  child-birth.  Oc- 
casionally it  extends 
entirely  across  and 
closes  the  orifice  al- 
together. This  con- 
dition is  spoken  of  as 
imperf orate  hymen. 

Glands.  —  In  con- 
nection with  the  vulva 
are  found :  — 

(1)  Vulvo-vaginal  glands  or  glands  of  Bartholin. 

(2)  Urethral  glands. 

The  vulvo-vaginal  are  two  round,  or  oval,  glands,  situated  on 
either  side  of  the  vagina.  Their  ducts  open  into  the  vulval  canal 
one  on  either  side,  in  the  groove  between  the  hymen  and  labia 
minora.  Their  secretion  lubricates  the  vulval  canal. 

The  urethral  glands  are  found  chiefly  beneath  the  walls  and 
floor  of  the  urethra.  They  secrete  mucus. 

Perineum.  —  The  perineum  bounds  the  external  outlet  of  the 
pelvis  and  constitutes  the  floor  of  the  genital  canal.  It  consists 
of  bands  of  muscular  tissue  strengthened  and  held  together  with 
fascia  and  covered  with  skin.  An  important  part  of  the  perineum 
is  the  triangular  portion  between  the  vagina  and  rectum.  It  is 
distensible  and  stretches  to  a  remarkable  extent  during  labor. 
Nevertheless  it  is  frequently  torn,  and  when  the  tear  is  of  any 


FIG.  223.  —  VULVA  OF  A  VIRGIN.  The  labia  have 
been  widely  separated.  Foss.  Nav.,  fossa  navicu- 
laris ;  Int.  Vag.,  introitus  vaginae;  Lab.  Min., 
labium  minus  ;  Vestib.,  vestibule.  (Gerrish.) 


472  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 

extent,  and  is  not  repaired,  the  vagina  and  uterus  lose  the  support 
afforded  by  it,  and  various  abnormal  conditions  follow. 


PHYSIOLOGY  OF  THE  FEMALE  GENERATIVE   ORGANS 

Functions.  —  The  functions  of  the  female  generative  organs  are  : 
(1)  the  formation  and  development  of  the  ovum,  (2)  the  reten- 
tion and  sustenance  of  the  fecundated  ovum  until  it  develops  into 
a  mature  foetus  ready  to  live  outside  the  body,  and  (3)  the  expul- 
sion of  the  foetus. 

Puberty.  —  Puberty  is  the  period  at  which  the  sexual  organs  be- 
come matured  and  functional  and  the  girl  develops  into  a  woman. 
The  event  is  not  accomplished  at  once,  but  extends  over  con- 
siderable time.  The  girl  undergoes  a  gradual  change  in  figure, 
the  hips  broaden,  the  breasts  develop,  and  for  the  first  time  a 
menstrual  flow  is  noticed.  At  first  the  menstrual  periods  are 
scanty  and  irregular,  but  after  a  few  months  they  settle  down 
to  the  characteristic  rate  and  duration.  In  temperate  climates 
the  age  at  which  girls  usually  attain  puberty  is  about  fourteen 
years.  In  southern  countries  it  is  somewhat  earlier,  and  in  the 
arctic  regions,  a  year  or  two  later.  However,  no  fixed  rule  can  be 
given,  as  the  time  of  arrival  at  puberty  varies  with  every  individual, 
depending  on  race,  temperament,  hygiene,  and  general  surround- 
ings. 

The  period  of  puberty  during  which  the  physical  changes  are 
occurring,  is  known  as  the  period  of  adolescence. 

Ovulation.  —  Ovulation  includes  the  process  of  the  develop- 
ment and  maturation  of  the  follicle  and  its  ovum,  and  the  rupture 
of  the  follicle. 

The  commonly  accepted  theory  is  that  about  or  shortly  before 
the  age  of  puberty,  the  Graafian  follicles  begin  to  discharge  their 
ova,  and  this  process  continues  until  the  menopause.  The  fre- 
quency with  which  well-developed  ova  are  discharged  is  the 
subject  of  much  dispute.  The  most  conservative  view  is  that 
there  is  one  mature  ovum  discharged  for  each  menstrual  epoch. 

Menstruation.  —  Menstruation  consists  of  the  periodical  dis- 
charge of  bloody  fluid  from  the  uterine  cavity.  When  once  es- 
tablished it  occurs  on  the  average  every  twenty-eight  days  from  the 
time  of  puberty  to  the  menopause,  with  the  exception  of  the  period 


CHAP.  XXI]    THE  ORGANS  OF  GENERATION  473 

of  pregnancy  and  lactation.  The  average  duration  is  from  four  to 
five  days  and  the  amount  of  blood  lost  is  from  four  to  six  ounces 
(120  to  180  cc.).  The  menstrual  fluid  consists  of  mucus,  epithelial 
cells,  and  blood.  Some  authorities  are  of  the  opinion  that  the 
mucous  membrane  of  the  uterus  is  normally  shed  during  this  pro- 
cess, others  do  not  share  this  opinion. 

The  menopause  or  climacteric.  —  By  menopause  or  climacteric 
is  meant  the  physiological  cessation  of  the  menstrual  flow,  and 
the  end  of  the  period  during  which  the  Graafian  follicles  develop 
in  the  ovaries,  and  consequently  the  end  of  the  child-bearing  period. 
It  is  marked  by  atrophy  of  the  breasts,  uterus,  tubes,  and  ovaries. 
The  age  of  menopause  varies  as  does  the  age  of  puberty ;  in  general, 
we  may  say  the  earlier  the  puberty  the  earlier  the  menopause,  and 
vice  versa.  In  temperate  climates  the  average  period  for  the  arrival 
of  the  menopause  is  at  the  age  of  forty-five  years.  - '  -1 , 

Changes  in  the  generative  organs  in  connection  with  menstrua- 
tion. —  At  the  beginning  of  menstruation  there  is  a  general  con- 
gestion of  the  generative  organs,  including  the  breasts,  accompanied 
by  more  or  less  discomfort  and  even  pain.  The  mucous  membrane 
of  the  uterus  undergoes  the  following  changes :  (1)  some  days  be- 
fore the  process  there  is  marked  hypertrophy  and  congestion  of 
the  mucous  membrane,  (2)  during  menstruation  there  is  capillary 
hemorrhage  and  the  epithelium  of  the  mucous  membrane  may  be 
cast  off,  (3)  during  the  week  following  menstruation  a  new  epithe- 
lium is  formed  and  the  mucous  membrane  returns  to  its  normal 
size,  (4)  a  period  of  rest  extends  to  the  next  period  of  congestion. 

Connection  between  ovulation  and  menstruation.  —  Whether 
ovulation  depends  upon  menstruation  or  menstruation  upon 
ovulation,  or  whether  either  has  any  connection  with  the  other, 
is  a  matter  of  lengthy  controversy.  At  the  present  time  the 
generally  accepted  view  is  that  menstruation  is  dependent  upon 
the  ovaries,  and  that  their  influence  is  exerted  through  the  medium 
of  the  blood.  It  is  thought  that  an  internal  secretion  is  formed  in 
the  ovaries ;  some  physiologists  think  by  the  cells  of  the  corpus 
luteum.  This  secretion  is  carried  to  the  uterus  by  the  blood  and 
is  responsible  for  the  hypertrophy  and  congestion  that  precedes 
menstruation.  So  far  it  has  not  been  possible  to  decide  whether 
the  internal  secretion  is  entirely  responsible  for  menstruation,  or 
whether  it  is  partly  due  to  a  power  inherent  in  the  uterine  muscle. 


474  ANATOMY  AND  PHYSIOLOGY     [CHAP.  XXI 

The  fact  that  operations  for  the  removal  of  the  ovaries  are  fol- 
lowed by  atrophy  of  the  uterus  and  cessation  of  menstruation, 
supports  the  theory  that  the  ovaries  are  in  some  way  responsible 
for  menstruation. 

Purpose  of  menstruation.  —  The  purpose  of  the  hypertrophy 
and  congestion  of  the  uterus  is  thought  to  be  nature's  way  of 
preparing  the  uterine  walls  for  the  reception  of  the  ovum  should 
it  become  fertilized. 

Mammary  glands.  —  The  two  mammary  glands,  or  breasts, 
may  be  considered  as  accessory  organs  of  generation. 

Function.  —  The  function  of  the  mammary  glands  is  to  secrete 
the  milk  which  is  needed  for  the  nourishment  of  the  young 
infant. 

Location.  —  Each  breast  covers  a  nearly  circular  space  in  front 
of  the  pectoral  muscles,  extending  from  the  second  to  the  sixth 
rib,  and  from  the  sternum  to  the  border  of  the  arm-pit. 

Structure.  —  The  breasts  are  convex  in  shape,  are  covered  ex- 
ternally by  skin,  and  about  the  centre  of  the  convexity  a  papilla 
projects,  which  is  called  the  nipple.  The  nipple  contains  the 
openings  of  the  milk  ducts,  and  is  surrounded  by  a  small  circular 
area  of  pink  or  dark  colored  skin,  which  is  called  the  areola.  They 
are  compound  glands,  and  are  divided  by  connective  tissue  parti- 
tions into  about  twenty  lobes,  each  of  which  possesses  its  own  ex- 
cretory duct,  which  as  it  approaches  the  top  of  the  breast  dilates 
and  forms  a  small  reservoir  in  which  milk  can  be  stored  during 
the  period  when  the  gland  is  active.  Each  duct  opens  by  a  sepa- 
rate orifice  upon  the  surface  of  the  nipple.  The  lobes  are  subdi- 
vided, and  the  small  lobes,  or  lobules,  are  made  up  of  the  terminal 
tubules  of  the  duct,  which  lie  in  a  mesh  of  fibrous  areolar  tissue 
containing  considerable  fat. 

Blood-vessels  and  nerves.  —  The  mammary  glands  are  well 
supplied  with  blood  brought  to  them  by  branches  of  the  axillary, 
internal  mammary,  and  intercostal  arteries.  The  nerves  are 
chiefly  intercostal  nerves. 

Development  of  the  mammary  glands.  —  The  increase  in  the 
size  of  the  mammary  glands  at  the  time  of  puberty  is  due  to  an 
increased  development  of  the  connective  tissue  and  fat.  The 
glandular  tissue  remains  undeveloped  and  does  not  function  unless 
conception  takes  place.  When  conception  occurs  the  glandular 


CHAP.  XXI]    THE  ORGANS   OF  GENERATION 


475 


tissue  undergoes  a  process  of  gradual  development  that  produces 
marked  changes.  The  breasts  become  larger  and  harder,  the 
veins  on  the  surface  become  more  noticeable,  the  areola  becomes 
enlarged  and  darkened,  the  nipple  becomes  more  prominent,  and 
toward  the  end  of  pregnancy  a  fluid  called  colostrum  can  be 


CLAVICLE 


PCCTORALIS   MAJOR 


SKIN 


FIBROUS  SEPTUM 
GLAND  SUBSTANCE 

A'DIPOSC   TISSUE 


IRO   RIB 


REOLAR  TISSUE 


FIRST 
RIB 


SECOND 

RIB 
PECTORALIS 

MINOR 

INTERCOSTALE9 
SHEATH  OF  PEC- 
TORALIS MAJOR 


SUPERFICIAL 
FASCIA 


FOURTH    RIB 


LUNG 

ADIPOSE   TISSUE 
HORIZONTAL  PLANE 
OF   NIPPLE 


FIFTH    RIB 


FIG.  224.  —  RIGHT   BREAST  IN   SAGITTAL   SECTION,   INNER  SURFACE  OF  OUTER 

SEGMENT.     (Gerrish.) 

squeezed  from  the  orifice  of  the  ducts.  After  delivery  the  amount 
of  colostrum  increases  for  a  day  or  two,  and  then  its  composition 
changes  to  that  of  milk. 

The  primary  development  and  later  functioning  of  the  mam- 
mary glands  suggests  an  intimate  connection  between  these  glands 
and  the  uterus  and  ovaries.  The  present  theory  is  that  the  in- 
crease in  the  size  of  the  breasts  at  the  time  of  puberty  is  influenced 


476  ANATOMY  AND   PHYSIOLOGY    [CHAP.  XXI 

by  the  internal  secretion  of  the  ovaries,  for  if  the  ovaries  are  re- 
moved before  puberty,  the  breasts  do  not  develop,  or  if  the  ovaries 
are  removed  after  puberty,  the  breasts  are  apt  to  atrophy.  The 
development  of  the  glandular  tissue  that  follows  conception  is 
thought  to  be  due  to  some  chemical  substance,  e.g.,  a  hormone, 
that  results  from  the  metabolism  of  the  foetus.  The  chemical 
nature  of  this  substance  is  not  known,  but  presumably  it  stimulates 
the  development  of  the  gland,  and  also  prevents  secretion,  as 
active  secretion  does  not  commence  until  after  delivery,  and  if 
conception  occurs  during  the  months  of  lactation,  the  character 
of  the  milk  is  changed  and  its  secretion  checked.  The  stimulus 
which  causes  the  active  secretion  of  milk  is  thought  to  result  from 
the  emptying  of  the  milk  ducts,  because  of  the  fact  that  when  a 
woman  does  not  nurse  her  infant,  the  secretion  of  milk  is  checked, 
and  the  breasts  return  to  their  usual  size.  The  active  secretion 
of  milk  is  also  influenced  by  the  nervous  system,  and  this  influence 
is  probably  exerted  through  the  vasomotor  nerves  which  control 
the  size  of  the  blood-vessels,  and  consequently  the  amount  of 
blood  sent  to  the  gland. 

The  secretion  of  milk.  —  The  secretory  portion  of  the  mammary 
glands  is  the  milk  ducts,  and  these  are  lined  with  secreting  cells. 
Some  of  the  constituents  of  the  milk,  i.e.,  water,  salts,  and  sugar, 
are  secreted  by  these  cells  from  the  blood,  but  it  is  thought  that  the 
cells  themselves  disintegrate  and  form  the  proteins  and  fat.  The 
sugar  contained  in  the  milk  is  lactose,  and  the  sugar  of  the  blood 
is  glucose,  so  if  the  first  is  derived  from  the  second,  some  chemical 
change  must  take  place  either  during  or  after  secretion. 

Colostrum  and  milk.  —  The  secretion  of  the  mammary  glands 
during  the  first  few  days  of  lactation  is  called  colostrum.  It  is  a 
thin,  yellowish  fluid,  composed  of  proteins,  fat,  sugar,  salts,  and 
water,  but  not  in  the  same  proportion  as  in  milk.  It  also  contains 
numerous  cells  containing  large  masses  of  fat.  These  are  called 
colostrum  corpuscles,  and  are  secreting  cells  that  are  not  completely 
broken  down. 

Human  milk  is  specially  adapted  to  the  requirements  of  the 
infant  and  so  differs  in  some  respects  from  that  of  all  other  animals. 
Cow's  milk  is  most  frequently  substituted  for  human  milk  and 
the  relative  composition  of  the  two  can  be  seen  in  the  following 
table :  — 


CHAP.  XXI]    THE   ORGANS   OF   GENERATION 


477 


HUMAN  (average) 

Cow's  (average) 

Water    

87-88% 

87.00% 

2-3% 

4.00% 

Fat                   

3-4% 

4.00% 

Lactose                               .... 

6-7% 

4.30% 

Salts 

2-3% 

070% 

In  substituting  cow's  milk  for  human  milk  the  differences  that 
must  be  taken  into  consideration  are  not  only  the  different  relative 
proportions,  but  also  the  following :  (1)  the  difference  in  the  pro- 
teins ;  the  protein  of  human  milk  is  one-third  caseinogen,  and  two- 
thirds  lactalbumin,  and  that  of  cow's  milk  is  five-sixths  caseinogen 
and  one-sixth  lactalbumin ;  (2)  the  difference  in  the  curds  formed 
in  the  stomach ;  human  milk  curdles  in  small  flocculi,  and  cow's 
milk  curdles  in  large  heavy  curds;  and  (3)  the  reaction  of  both 
human  and  cow's  milk  is  amphoteric,  but  cow's  milk  is  more 
nearly  acid  than  human  milk. 

Male  generative  organs.  —  The  male  generative  organs  con- 
sist of  the  following  structures  :  — 

Testes,  two   glandular   organs   which   produce  the  sper- 
matozoa. 
Vas  Deferens. 
Seminal  Vesicles. 
Ejaculatory  Ducts. 
The  Spermatic  Cords. 
The  Penis. 
The  Prostate  Gland. 
Cowper's  Glands. 

Testes.  —  The  testes  are  two  glandular  organs  which  are  sus- 
pended from  the  inguinal  region  by  the  spermatic  cords,  and  are 
surrounded  and  supported  by  the  scrotum.  Each  gland  weighs 
from  six  to  eight  drachms  (22  to  30  gms.)  and  consists  of  two 
portions :  (1)  the  testicle  proper,  and  (2)  the  epididymis. 

(1)  The  testicle  proper  is  ovoid  in  shape  and  covered  exteriorly 
by  fibrous  tissue  which  sends  incomplete  partitions  into  the  cen- 
tral portion  of  the  gland,  dividing  it  into  communicating  cavities. 
In  these  cavities  are  winding  tubules  which  are  surrounded  by 
blood-vessels  and  held  together  by  interstitial  tissue.  These 


478 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 


tubules  inosculate  in  a  sort  of  mesh  (rete  testis)  and  finally  all 

unite  in  the  epididymis. 

(2)  The  epididymis  is  a  long,  narrow  body  which  lies  along  the 

posterior  portion  of  the  testicle  and  consists  of  a  tortuous  tubule, 

which  is  lined  with  mucous  membrane,  and  contains  some  muscular 

tissue  in  its  walls.  If 
unravelled  it  is  found  to 
be  about  twenty  feet 
(5  metres)  long.  It  con- 
nects the  testicle  proper 
with  the  vas  deferens. 

Function.  —  The  func- 
tion of  the  testes  is  the 
production  of  sperma- 
tozoa. These  sperma- 
tozoa are  the  essential 
part  of  the  seminal  fluid. 
The  spermatozoa  origi- 
nate in  the  cells  of  the 
testes  lining  the  tubules 
which  compose  the  bulk 
of  the  testes.  An  in- 
ternal secretion  is  also 
supposed  to  be  formed 
here. 


"Prepuce 

FIG.  225.  —  MALE  SEXUAL  APPARATUS. 


(Hall.) 


Descent  of  the  testes.  —  In  early  foetal  life  the  testes  are  abdom- 
inal organs  lying  in  front  of  and  below  the  kidneys.  During 
the  process  of  growth  they  are  drawn  downward  through  the 
inguinal  canal  and  shortly  before  birth  are  normally  found  in 
the  scrotum.  Sometimes,  particularly  in  premature  infants, 
a  testis  is  found  in  the  inguinal  canal  or  even  in  the  abdominal 
cavity;  as  a  rule  it  soon  descends  and  occupies  its  proper 
position ;  but  occasionally  it  does  not  descend  and  an  operation 
is  necessary. 

The  Vas  Deferens.  —  The  vas  deferens  is  a  continuation  of  the 
epididymis,  and  is  the  excretory  duct  of  the  testicle.  After  a  very 
devious  course  it  joins  the  duct  of  the  seminal  vesicle  at  the  base 
of  the  bladder.  It  consists  of  three  coats,  an  external  areolar,  a 
middle  muscular,  and  an  internal  mucous  coat. 


CHAP.  XXI]    THE  ORGANS  OF  GENERATION  479 

The  Seminal  Vesicles.  —  The  seminal  vesicles  are  two  pouches 
which  are  placed  each  one  on  the  outer  side  of  each  vas  deferens, 
between  the  bladder  and  the  rectum.  They  are  pyramidal  in  form, 
with  the  broad  ends  directed  backward  and  widely  separated. 
The  anterior  portions  converge,  become  narrowed,  and  unite  on 
either  side  with  the  corresponding  vas  deferens  to  form  the  ejacu- 
latory  duct. 

Function.  —  The  seminal  vesicles  serve  as  a  reservoir  for  the 
semen,  to  which  they  add  a  secretion  of  their  own. 

The  Ejaculatory  Ducts.  —  The  ejaculatory  ducts  are  two  in  num- 
ber, one  right  and  the  other  left.  They  are  formed  by  the  union 
of  the  seminal  vesicle  and  vas  deferens  of  each  side.  They  run 
downward  and  converge  as  they  descend,  enter  and  pass  between 
the  lobes  of  the  prostate  gland  and  open  into  the  floor  of  the  pros- 
tat  ic  portion  of  the  urethra.  Each  has  an  external  areolar,  middle 
muscular,  and  internal  mucous  coat. 

The  scrotum.  —  The  scrotum  is  a  pouch  which  contains  the 
testes  and  a  part  of  each  spermatic  cord.  It  consists  of  a  layer 
of  skin,  and  the  dartos.  The  skin  is  thick  and  dark,  presents  folds 
or  rugae,  is  furnished  with  sebaceous  glands,  and  covered  with  short 
hairs.  The  dartos  is  a  thin  tunic  of  a  reddish  color  consisting  of 
muscular  fibres  and  elastic  tissue  and  containing  numerous  blood- 
vessels. It  is  continuous  with  the  superficial  fascia  of  the  groin 
and  perineum.  It  sends  in  a  partition,  which  separates  the  two 
testes. 

The  Spermatic  Cord.  —  The  spermatic  cord  forms  the  pedicle 
of  each  testis  and  extends  from  the  internal  abdominal  ring  to  the 
back  of  the  testis.  Each  cord  consists  of  the  vas  deferens,  arteries, 
veins,  lymphatics,  nerves,  the  layers  of  fascia  which  cover  the 
testis,  and  the  remains  of  the  peritoneal  testicular  process.  These 
parts  are  connected  together  by  areolar  tissue. 

The  Penis.  —  The  penis  consists  of  three  more  or  less  cylindrical 
bodies  of  erectile  l  tissue  enclosed  in  fibrous  sheaths.  The  two 
corpora  cavernosa  lie  above  the  corpus  spongiosum,  in  which 
the  urethra  is  contained.  The  glans  penis  is  continuous  with 


1  Erectile  tissue  is  found  in  the  clitoris,  penis,  and  the  nipples.  The  form,  size, 
and  consistency  of  this  tissue  changes  according  to  the  amount  of  blood  contained 
in  it.  An  increased  amount  of  arterial  blood  causes  swelling,  and  consequent  press- 
ure on,  and  occlusion  of,  the  veins. 


480  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 

the  corpus  spongiosum.  The  covering  of  the  penis  is  of  loose 
skin,  but  over  the  glans  penis,  and  lining  the  prepuce,  it  re- 
sembles mucous  membrane.  In  this  region  there  is  an  abundant 
subcutaneous  nerve  plexus  and  numerous  Pacinian1  corpuscles, 
so  that  it  is  possessed  of  acute  sensibility. 

The  urethra  extends  from  the  bladder  through  the  corpus 
spongiosum  to  the  end  of  the  penis.  It  is  usually  divided  into 
three  parts  :  (1)  the  prostatic  urethra,  (2)  the  membranous  urethra, 
and  (3)  the  penile  or  spongy  portion.  The  length  is  usually  given 
as  eight  inches  (20  cm.),  a  large  part  of  which  lies  inside  the  pelvis. 
It  is  lined  with  mucous  membrane  and  furnished  with  numerous 
muscular  fibres. 

The  Prostate.  —  The  prostate  gland  is  situated  in  front  of  the 
neck  of  the  bladder  and  around  the  commencement  of  the  urethra. 
It  resembles  a  chestnut  in  form  and  consists  of  a  dense  fibrous 
capsule  containing  glandular  and  muscular  tissue.  The  glandular 
tissue  consists  of  tubules  which  communicate  with  the  urethra 
by  minute  orifices. 

Function.  —  The  function  of  the  prostate  gland  is  to  secrete 
the  prostatic  fluid,  which  is  an  essential  element  of  the  seminal 
fluid. 

Cowper's  glands.  —  These  are  two  small  bodies  about  the  size 
of  a  pea  situated  one  on  each  side,  adjacent  to,  and  opening  into 
the  membranous  urethra.  They  secrete  a  fluid  which  goes  to 
form  part  of  the  seminal  fluid. 

Puberty.  —  Puberty  is  the  period  at  which  the  sexual  organs 
become  matured  and  functional,  and  the  boy  develops  into  a  man. 
This  occurs  in  the  male  about  a  year  later  than  in  the  female,  about 
fifteen  years  of  age.  At  this  time  the  "  Adam's  apple  "  develops, 
producing  a  marked  change  in  the  voice,  the  external  genitals  grow 
somewhat  rapidly,  hair  grows  on  the  face,  pubes,  axillae,  and  other 
parts  of  the  body,  and  seminal  fluid  begins  to  be  secreted.  At  the 
same  time  sexual  desires  unknown  before  are  experienced. 

Semen.  —  The  semen  is  a  fluid  derived  from  the  various  sexual 
glands  in  the  male.  The  main  elements  in  this  fluid  are  the  sper- 
matozoa ;  the  other  constituents  are  derived  from  the  seminal 
vesicles,  prostate  gland,  and  Cowper's  glands. 

1  Pacinian  corpuscles  are  specialized  nerve-endings  found  in  the  genital  organs 
of  both  sexes,  also  in  the  palms  of  the  hands  and  the  soles  of  the  feet. 


CHAP,  xxi]  REPRODUCTION  48i 

PHYSIOLOGY  OF  REPRODUCTION 

Reproduction.  —  The  purpose  of  reproduction  is  the  continu- 
ation of  the  species,  and  is  accomplished  by  means  of  the  reproduc- 
tive organs,  whose  importance  is  in  their  adaptation  to  produce 
another  being.  The  reproduction  of  all  living  organisms  is  ac- 
complished in  two  ways  :  — 

(1)  Asexually;  (2)  sexually. 

(1)  In  the  asexual  type  one  individual  divides  into  two  or  more, 
as  is  seen  in  the  budding  of  plants  and  animals,  also  in  the  unicel- 
lular organisms  when  one  organism  constricts  itself  into  two,  either 
directly,  or  indirectly  by  mitosis,  or  divides  itself  up  into  a  number 
of  spores. 

(2)  In  the  sexual  type,  the  individuals  fuse  either  temporarily 
or  permanently  before  cell  division,  or  else  they  make  sex  cells 
(gametes)  which  fuse  to  form  the  new  individual.     In  many  of 
the  lower  organisms  these  sex  cells  are  shed  into  the  water  and 
there  unite.     In  most  of  the  higher  organisms  the  female  sex  cells 
or  ova  remain  in  the  female  organism,  and  the  male  sex  cells  are 
placed  in  the  reproductive  tract.     In  the  human  species  the  sperma- 
tozoa are  placed  in  the  vagina  at  the  mouth  of  the  uterus  and  swim 
upward  through  the  uterus  and  the  Fallopian  tubes,  in  or  near 
which  union  writh  the  ova  takes  place. 

Impregnation.  —  The  term  impregnation  or  fertilization  is 
applied  to  the  union  of  the  spermatozoon  or  male  cell  with  the 
ovum  or  female  cell. 

The  ovum.  —  The  ovum  is  a  minute  globular  cell  about  -^-5  inch 
(0.2  mm.)  in  diameter.  (See  Fig.  6  for  cell  structure.) 

The  spermatozoon.  —  The  spermatozoon  is  much  smaller  than 
the  ovum,  being  only  ^5-  inch  (0.05  mm.)  in  length.  It  consists 
of  an  elliptical  head,  a  rod-shaped  middle  piece,  and  a  tail  that 
gradually  tapers.  The  head  contains  nuclear  material  and  chro- 
matin.  There  is  an  active  vibratory  motion  of  the  tail  which 
allows  it  quite  free  motion  in  the  seminal  fluid.  Because  of  this 
free  motion  the  spermatozoa  are  able,  when  deposited  in  the  vagina, 
to  travel  upward  into  the  uterus,  and  into  the  tubes  even  against 
the  current  produced  by  the  cilia  of  the  tubes. 

Maturation  of  sex  cells.  —  Before  union  the  maturation  of  the 
sex  cells  takes  place.  In  this  process  the  number  of  chromosomes 
2i 


482  ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 

is  reduced  to  one-half  the  original  number.  Note  that  in  Fig.  8 
each  chromosome  is  divided  longitudinally  into  halves  so  that  each 
new  cell  has  the  same  number  of  chromosomes  as  the  original  cell. 
In  maturation  the  division  is  such  that  each  new  cell  has  one-half 
the  original  number  of  chromosomes.  Fusion  or  fertilization  re- 
stores the  normal  number  of  chromosomes.  Much  of  our  theory 
of  inheritance  is  based  upon  these  chromosomes,  and  the  fact  that 
they  are  contributed  to  the  individual,  half  by  the  sperm  cell  and 
half  by  the  ovum. 

Site  of  impregnation.  —  It  is  thought  that  impregnation  takes 
place  in  the  Fallopian  tubes  or  near  the  wall  of  the  ovaries.  When 
the  Graafian  follicle  ruptures  and  an  ovum  escapes  into  the  ab- 
dominal cavity,  the  current  produced  by  the  cilia  of  the  tubes  is 
thought  to  draw  it  into  the  tube.  Once  in  the  tube  the  peristaltic 
action  of  the  tube  and  the  action  of  the  cilia  propel  it  slowly  along 
to  the  uterus.  If  the  ovum  does  not  become  impregnated  it  passes 
into  the  uterus  and  is  cast  off  in  the  next  menstrual  flow.  If, 
however,  it  is  impregnated,  segmentation  or  the  process  of  cell 
division  begins  at  once. 

Segmentation.  —  The  impregnated  cell  (zygote)  rapidly  divides 
into  two,  each  of  these  two  into  other  two,  and  so  forth,  until  we 
have  a  number  of  cells  where  formerly  there  was  one.  At  this 
stage  the  collection  of  cells  is  called  the  blastoderm.  Gradually 
these  cells  which  constitute  the  blastoderm  become  arranged  in 
three  layers,  the  outer  called  the  ectoderm,  an  inner  called  the  ento- 
derm,  and  a  middle  layer  called  the  mesoderm.1  Later  the  organs 
are  formed  by  the  folding  off  of  these  tissues,  and  as  the  embryo 
grows  it  takes  on  the  form  of  the  adult. 

The  passage  of  the  fertilized  ovum  through  the  tubes  requires 
about  eight  days,  and  during  this  time  many  thousands  of  cells 
are  formed  and  enclosed  in  a' sac  called  the  amnion.  The  collec- 
tion of  cells  surrounded  by  the  amnion  is  called  an  embryo.  After 
entering  the  uterus  the  embryo  attaches  itself  to  the  mucous  mem- 
brane, in  the  upper  portion,  usually  near  the  opening  of  the  Fal- 
lopian tubes. 

Changes  in  the  uterine  lining.  —  The  preparation  of  the  mucous 
membrane  of  the  uterus  for  the  reception  of  the  impregnated  ovum 
includes  changes  that  are  similar  to  those  that  precede  menstrua- 

1  See  page  28. 


CHAP.  XXI]  REPRODUCTION  483 

tion.  The  mucous  membrane  becomes  softer,  thicker,  and  highly 
congested.  In  this  condition  it  is  known  as  the  decidua  vera,  and 
the  point  to  which  the  ovum  becomes  attached  and  which  later 
develops  into  the  placenta  is  called  decidua  serotina. 

Intrauterine  growth.  —  During  the  period  of  intrauterine  life 
growth  takes  place  rapidly.  From  the  union  of  the  ovum,  which 
is  ri?  mch  (0.2mm.)  in  diameter,  and  the  spermatozoon,  which  is 
much  smaller,  there  is  developed  in  two  weeks'  time  an  embryo 
which  is  about  -J-  of  an  inch  (6.25  mm.).  At  the  end  of  four  weeks 
it  is  about  £  inch  (12.5  mm.)  long,  and  at  four  months  it  is  called 
a  foetus,  because  it  has  the  appearance  of  a  human  being,  with 
well-developed  eyes,  fingers  and  toes  separated,  and  the  external 
genitals  sufficiently  formed  to  determine  the  sex.  The  usual  du- 
ration of  pregnancy  is  ten  lunar  or  nine  calendar  months.  At  the 
end  of  six  months  the  foetus  is  sufficiently  developed  to  live  out- 
side the  mother's  body,  but  it  is  frail  and  requires  a  great  deal  of 
care. 

For  further  details  on  the  subject  of  reproduction  the  student  is 
referred  to  standard  works  on  physiology  and  obstetrics. 


484 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 


Female 

Generative 

Organs 


Internal 
Organs 


External 
Organs 


SUMMARY 

Ovaries  —  two  glandular  organs  in  which  the 

ova  are  formed. 
Fallopian  tubes  —  two  canals  through  which  the 

ova  reach  the  uterine  cavity. 
Uterus  —  a  hollow,   pear-shaped  organ  which 

receives  the  ovum. 
Vagina  —  a  canal  that  extends  from  the  uterus 

to  the  vulva. 
Mons  Veneris  —  a  cushion  of  areolar,  fibrous 

and  adipose  tissue,  in  front  of  pubic  bones, 

covered  with  skin  and  after  puberty  with  hair. 
Labia  majora  —  two  folds  that  extend  from  the 

mons  Veneris  to  within  an  inch  of  the  anus. 
Labia  minora  —  two  folds  situated  between  the 

labia  majora. 
Clitoris  —  small  body,  situated  at  apex  of  the 

triangle  formed  by  junction  of  labia  minora. 

Well  supplied  with  nerves  and  blood-vessels. 
Hymen  —  fold  of  mucous  membrane  that  sur- 
rounds vaginal  orifice. 

Vulvo-vaginal  —  oval  bodies  situated 

on  either  side  of  the  vagina. 
Urethral  —  glands  found   chiefly  be- 
neath the  walls  and  floor  of  urethra. 


Attached 


Size 


Ovaries 


Two  almond-shaped  glandular  bodies. 
Situated  in  posterior  fold  of  broad  ligament. 

To  uterus  —  by  ligament  of  ovary. 
To  tubes  —  by  fimbria?. 
1^  inches  long. 
|  inch  wide. 
£  inch  thick. 
Weight  —  1-2  drachms. 

Fibrous  tissue. 
Blood-vessels. 
Lymphatics. 
I  Nerves. 
Graaf- 
ian 
fol- 
licles 

Covering  of  germinal  epithelium. 
|  Produce,  develop,  mature,  and  discharge  ova. 
I  Form  an  internal  secretion. 


Structure 


Stroma 


1.  Outer  coat  fibrous  tissue. 

2.  Inner  layer  of  cells  contain  ovum. 


Function 


CHAP.  XXI] 


SUMMARY 


485 


Location 


Divisions 


Three 
Coats 


Enclosed  in  layers  of  broad  ligament. 
Extend  from  upper  angles  of  uterus  to  sides  of 
pelvis. 

1 .  Isthmus  —  or  inner  constricted  portion  near 

uterus. 

2.  Ampulla  —  dilated    portion    which    curves 

over  ovary. 

3.  Infundibulum  —  trumpet-shaped    extremity 

—  fimbrise. 

1.  External,  or  serous. 

2.  Middle,  or  muscular. 

3.  Internal,  or  mucous,  arranged  in  longitudinal 

folds  and  covered  with  cilia. 
Function  —  Convey  ova  to  uterus. 
Hollow,  thick-walled  organ,  placed  in  pelvis  between  bladder 

and  rectum. 
Fundus  =  rounded  upper  portion,   above  the 

entrance  of  the  tubes. 
Body  =  portion  below  fundus,  above  neck. 
Cervix  =  lower  and  smaller  portion  which  ex- 
tends into  vagina. 
External,  or  serous,  derived  from  peritoneum. 

Circular  layer          j  Interlaced      in 
Muscular    Longitudinal  layer  \      every    direc- 

Spiral  layer  J      tion. 

Mucous  membrane,  lines  the  uterus. 
Uterine  arteries  from  internal  iliacs. 
Ovarian  arteries  from  aorta. 
Remarkable  for  tortuous  course  and  frequent 

anastomoses. 

Broad,  or  lateral  —  two  layers  of  serous  mem- 
brane. 

Round  —  two  fibro-muscular  cords. 
Utero-sacral  —  two  partly  serous,  partly  mus- 
cular, ligaments. 
Anterior  —  peritoneal  floor  of  the  utero-vesical 

pouch. 
Recto-vaginal  —  peritoneal  floor  of  the  recto  - 

vaginal  pouch. 

To  receive  ovum,  and  if  it  becomes  fertilized  to 
retain  it  until  developed  and  then  to  expel  it. 
Canal  —  Extends  from  uterus  to  vulva. 
Outer  coat  is  fibrous. 
Middle  coat  is  muscular. 
Mucous  coat,  or  lining,  arranged  in  rugae. 
Location  —  Placed  between  urethra  and  rectum. 


Divisions 


Three 
Coats 


Blood- 
vessels 


Ligaments 


Function 


Three 
Coats 


486 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XXI 


Function 


Ovulation 


Formation  and  development  of  ovum. 
Retention  and  sustenance  of  fecundated  ovum. 
Puberty  —  Age  at  which  sexual  organs  become  matured  and 
functional.     Girl  changes  to  woman. 

Process  of  development  and  maturation  of  fol- 
licle and  ovum,  and  discharge  of  ovum. 

from  the  uterus.  Occurs  on  an 
y  twenty-eight  days.  Extends 
?  (14  years)  to  the  menopause, 
3  (about  45  years).  This  repre- 
.d-bearing  period  of  a  woman's 

1.  General  congestion  of  gener- 

ative    organs,      including 
breasts. 

2.  Hypertrophy  and  congestion 

of   mucous    membrane    of 
uterus. 

3.  Capillary  hemorrhage.     Epi- 

thelium is  cast  off. 

4.  Following  menstruation  a  new 

epithelium  is  formed. 
Probably  dependent  on  internal 
secretion  of  ovaries,  and  pos- 
sibly is  aided  by  power  in- 
herent in  uterine  muscle. 
,ure's  way  of  preparing  uterine 
iption  of  fertilized  ovum. 
Menopause  —  Physiological  cessation  of  the  menstrual  flow. 
Accessory  organs  of  generation. 
Function  —  To  secrete  milk  to  nourish  infant. 
f  Extend  from  second  to  sixth  rib. 
1  Sternum  to  arm-pit. 

Outer  surface  convex  —  papilla  projects  from 
centre  —  called  nipple  —  contains  openings 
of  milk  ducts.  Nipple  surrounded  by  areola. 

1 .  Consists  of  connective  tissue  framework  which 

divides  the  gland  into  about  twenty  lobes. 

2.  Lobes  are  subdivided  into  lobules. 

3.  Lobules  are  made  up  of  terminal  tubules 

of  the  duct. 

4.  Each  lobe  possesses  its  own  excretory  duct, 

which  is  called  lactiferous  and  is  sacculated. 
Axillary. 

Internal  mammary. 
Intercostal. 


A  flow  of  blooc 

average  evei 

from  pubert 

or  climacteri 

sents  the  chi 

life. 

Physiology 

of  Gen- 

erative 
Organs 

Menstrua- 

Changes in 
connection 

tion 

with  men- 

struation 

. 

Connection 

between  ovu- 

lation  and 

menstruation 

Purpose  —  Na 

walls  for  rec< 

Location 


Mammary 
Glands 

Structure 

Blood- 
vessels 

CHAP.  XXI] 


SUMMARY 


487 


Mammary 
Glands 


Colostrum 


Milk 


Male 

Generative 

Organs 


Nerves  —  Intercostal. 

Primary  development  at  time  of  puberty,  prob- 
ably due  to  internal  secretion  of  ovaries. 

Functional  development  follows  conception, 
probably  due  to  chemical  substances  that 
result  from  metabolism  of  fcetus.  Active  se- 
cretion stimulated  by  emptying  milk  ducts 
and  influenced  by  nervous  system. 

Water 

Secreted  from  blood. 


Develop- 
ment 


Secretion 
of  milk 


Salts 
Sugar 
Proteins 
Fat 


Formed    by    disintegration    of 
cells  lining  lactiferous  tubules. 


Thin  yellowish  fluid  secreted  during  first  few  days  of  lactation. 

Proteins 5.71  per  cent 

Fat 2.04  per  cent 

Composi-  \  Sugar 3.74  per  cent 

tion  Salts 0.28  per  cent 

Water 88.23  per  cent 


Composi- 
tion 


Differ- 
ences 


Human  Cow's 

Water 87-88%  87.00% 

Proteins 2-3%  4.00% 

Fat        3-4%  4.00% 

Lactose 6-7%  4.30% 

Salts 2-3%  0.70% 

Different  relative  proportions. 

\  Caseinogen 

Human <         ,  „  . 


Difference  in 
proteins 


Difference  in 
reaction 


I  Lactalbumin  f . 

Cow's    I  Casein°gen  *• 
\  Lactalbumin  £. 

Difference  in  /  Human  —  small  flocculi. 
curds          1  Cow's  —  heavy  curds. 
Human  —  amphoteric. 
Cow's  —  amphoteric,  but  more 
nearly  acid. 


Testes. 

Vas  deferens. 

Seminal  vesicles. 

Ejaculatory  ducts. 

Spermatic  cords. 

The  penis. 

The  prostate  gland. 

Cowper's  glands. 


488 


ANATOMY  AND   PHYSIOLOGY     [CHAP.  XXI 


Testes 


Structure 


Two  glandular  organs  which  produce  the  spermatozoa. 

Testicle  proper  —  ovoid  body  covered  by  fibrous 
tissue.  Central  portion  consists  of  irregular 
cavities  filled  with  seminiferous  tubules  and 
blood-vessels. 

Epididymis  —  tortuous   .tubule,     forms    long, 
narrow  body  which  lies  along  posterior  por- 
tion of  testes. 
f  In  early  foetal  life  in  abdomen  below  kidneys. 
Location     <  Before  birth  are  normally  drawn  downward  to 
I     scrotum,  and  are  suspended  by  spermatic  cord. 
f  Production  of  spermatozoa. 
I  Production  of  internal  secretion. 


Function 


Vas  Defer  ens  —  Continuation  of  epididymis,  and  serves  to  connect  the 
epididymis  and  the  seminal  vesicle  of  each  side. 


Seminal 
Vesicles 


Ejaculatory 
Ducts 


Scrotum 


Spermatic 
Cords 


Penis 


Two  pouches  located  between  bladder  and  rectum  on  outer 
side  of  each  vas  deferens.  Connect  vas  deferens  with 
ejaculatory  duct. 

Function  —  Serve  as  reservoirs  for  semen,  to  which  they  add 
a  secretion  of  their  own. 

Formed  by  union  of  seminal  vesicles  and  vas  deferens  of 

each  side. 
Run  downward,  converge,  pass  between  lobes  of  prostate 

gland  and  open  into  the  floor  of  the  prostatic  portion  of 

the  urethra. 

Pouch  which  contains  testes  and  part  of  each  spermatic  cord. 
Covered  with  thick  dark  skin. 
Dartos  —  reddish   tunic  under   skin,   consists 
Structure    <      of  muscular  and  elastic  tissue  with  numer- 
ous blood-vessels.     Divided  by  septum  into 
halves. 

Consists  of  the  vas  deferens,  arteries,  veins,  lymphatics, 
nerves,  and  layers  of  fasciae  connected  by  areolar  tissue. 
Serve  as  pedicles  for  testes. 

Extends  from  the  internal  abdominal  ring  to  the  back  of 
the  testes. 

Consists  of  three  cylindrical  f  Two  corpora  cavernosa,  and 
bodies  of  erectile  tissue  I  one  corpus  spongiosum. 

Contains  urethra  which  extends  from  bladder  to  the  end  of 
penis. 

Covered  with  skin  and  mucous  membrane. 


CHAP.  XXI] 


SUMMARY 


489 


Urethra 


Extends  from  the  bladder  through  the  corpus  spongiosum 
to  the  end  of  the  penis.     Length,  8  inches. 

Prostatic  portion. 
Divisions         Membranous  portion. 

Penile  or  spongy  portion. 
Consists        f  Mucous  lining, 
of  Numerous  muscular  fibres. 


The  Pros- 
tate 


Situated  in  front  of  the  neck  of  the  bladder  and  around  the 

commencement  of  urethra. 
Shape  —  resembles  chestnut. 

f  Fibrous  capsule  containing  glandular  and  mus- 
Consists  of    ]      cular  tissue.     Glandular  tissue  consists  of 

tubules  which  empty  into  urethra. 
Function  —  Secretion  of  prostatic  fluid. 


Cowper's 
Glands 


Located  one  on  each  side  of  membranous  urethra,  into  which 

they  empty.    About  the  size  of  a  pea. 
Function  —  Secretion  of  a  fluid  which  forms  part  of  seminal 

fluid. 


Puberty 


j  Age  at  which  sexual  organs  become  matured  and  functional. 
1  Boy  changes  to  a  man. 


Semen 


f  Fluid  derived  from  the  various  sexual  glands  in  the  male. 
1  Spermatozoa  are  the  main  elements. 


Reproduc- 
tion 


Function  —  Produce  another  being. 


Accom- 
plished 
in  two 
ways 


Asexually 


Sexually 


1.  Divide   into   two   or   more,  e.g., 

budding  of  plants  and  animals. 

2.  Divide    in   two    directly    or    by 

mitosis. 

3.  Divide  into  spores. 

1.  Individuals  fuse  permanently  or 

temporarily. 

2.  Make  sex  cells  (gametes). 

(a)  In  lower  organisms  shed  in 
water  and  unite. 

(6)  In  higher  organisms  gamete 
retained  by  female,  and 
male  gamete  is  placed  in  re- 
productive tract  of  female. 


490 


ANATOMY  AND   PHYSIOLOGY    [CHAP.  XXI 


Impregna- 

tion 

Sperma- 

tozoon 

Consists  of 


Maturation 
of  Sex 
Cells 


Union  of  spermatozoon  and  ovum. 

Occurs  in  the  Fallopian  tubes  or  near  the  wall  of  the  ovaries. 
Ovum  —  Globular    cell   formed    in    ovaries    ris    inch   in 
diameter. 

A  long,  narrow  cell  formed  in  testes,  -sk*  of  an 
inch  in  length. 

Elliptical    head    which     contains 
nuclear  material  and  chromatin. 
Rod-shaped  centre  piece. 
.Tail. 
Capable    of    independent    motion   in   a   fluid 

medium. 
Function  —  to  fertilize  ovum. 

Reduction  of  chromosomes  in  each  sex  cell  to  one-half  the 

original  number. 
Union  of  sex  cells  restores  original  number,  hence  one-half 

contributed  by  each  sex. 
Theory  of  inheritance  based  on  chromosomes. 


Develop- 
ment of 
Zygote 


1.  Impregnated  cell  divides  into  many  cells. 

called  blastoderm. 

Entoderm. 

2.  Blastoderm  composed  of    Mesoderm. 

Ectoderm. 

3.  Tissues  are  folded  off  to  form  organs. 

4.  In  two  weeks  time  embryo  is  |  inch  long. 

5.  In  four  weeks  tune  embryo  is  \  inch  long. 

6.  At  four  months  called  a  foetus. 


Collection 


METRIC  SYSTEM 


LI 


Millimetres 


Square 
Centi- 
metre 


11 


|4  5 

Centimetres 


I  9        10 


The  area  of  the  figure  within  the  heavy  lines  is  that 
of  a  square  decimetre.  A  cube,  one  of  whose  sides  is 
this  area,  is  a  cubic  decimetre  or  litre.  A  litre  of  water 
at  the  temperature  of  4°  C.  weighs  a  kilogramme. 

A  litre  is  2.11  pints  or  33.81  ounces.  A  pint  is  0.473 
of  a  litre.  (Liquid  measure.) 

A  litre  is  1.76  pint.  A  pint  is  0.568  litre.  (Dry 
measure.) 

The  smaller  figures  in  dotted  lines  represent  the  areas 
of  a  square  centimetre  and  of  a  square  inch. 

A  cubic  centimetre  of  water  at  4°  C.  weighs  a  gramme. 


Square  Inch 


1  Metre  =  39.370432  inches. 

1  Decimetre  =    3.937043  inches. 
1  Centimetre  =      .393704  inch. 
1  Millimetre  =     .039370  inch. 


1  Gramme 
1  Decigramme 
1  Centigramme 
1  Milligramme 
1  Dekagramme 
1  Hektograinme 
1  Kilogramme 
1  Kilogramme 
1  Kilogramme 


15.432  grains. 
1.543  grains. 
.154  grain. 
.015  grain. 
154.323  grains. 
1543.235  grains. 
15432.350  grains. 
35.274  ounces. 
2.204  pounds. 


Avoirdupois  weights  are  used  in  weighing  the  organs  of  the  body.    One  ounce 
avoirdupois  =  28.35  grammes. 


GLOSSARY 

Abduc'tion.     Drawn  away  from  the  middle  line  of  the  body. 

Acromeg'aly.  A  disease  characterized  by  an  overgrowth  of  the  extremi- 
ties and  the  face  as  well  as  the  soft  parts. 

Adduction.     Brought  to  or  nearer  the  middle  line. 

Adre'nal.  A  small  gland  situated  on  the  top  of  the  kidneys.  Same  as 
supra-renal. 

Afferent.  Bearing  or  carrying  inwards,  as  from  the  periphery  to  the 
centre. 

Agglutination.  The  mutual  adhesion  or  clumping  of  foreign  cells,  and 
loss  of  motility  in  the  case  of  motile  bacteria,  when  suspended  in  fluid 
containing  a  suitable  agglutinin. 

Agglu'tinin.  A  substance  occurring  in  blood  plasma  which  produces  ag- 
glutination by  its  action  on  the  surface  of  foreign  cells. 

Aggregated.     Formed  by  a  collection  of  several  bodies ;   crowded. 

Ag'minated.  Arranged  in  clusters,  grouped  together,  as  the  agminated 
glands  of  Peyer  in  the  small  intestine. 

Albu'mins.  Thick,  viscous  substances  containing  nitrogen,  that  are  solu- 
ble in  water,  dilute  acids,  dilute  salines,  and  concentrated  solutions 
of  magnesium  sulphate  and  sodium  chloride.  They  are  coagulated 
by  heat  and  strong  acids.  Examples  are :  egg  albumin  and  serum 
albumin  of  blood. 

Albuminu'ria.     Presence  of  albumin  in  the  urine. 

Alimen'tary.     Pertaining  to  aliment,  or  food. 

Alve'olus,  pi.  Alve'oli.  Any  little  cell,  pit,  cavity,  fossa,  or  socket. 
Socket  of  a  tooth,  or  an  air-cell. 

Amito'sis.     Fission  or  direct  cell-division.     Same  as  akinesis. 

Amce'ba.  A  single-celled  organism,  which  is  constantly  changing  its  form 
by  protrusions  and  withdrawals  of  its  substance. 

Amphoter'ic.  Partly  acid  and  partly  alkaline  in  reaction;  having  the 
power  of  turning  red  litmus  paper  blue,  and  blue  litmus  paper  red. 

491 


492  GLOSSARY 

Ampul'la.    The  dilated  part  of  a  canal. 

Anab'olism.  The  process  by  means  of  which  simpler  substances  are  built 
up  into  more  complex  substances. 

Anastomo'sis.     Communication  of  branches  of  vessels  with  one  another. 

An'tigens.  Immunizing  substances  which,  when  introduced  into  the  body 
of  a  susceptible  animal,  may  produce  specific  antibodies. 

An'trum.  A  cavity;  applied  especially  to  one  in  the  upper  maxillary 
bone,  termed  antrum  of  Highmore. 

Aponeuro'sis.  A  flat  wide  band  of  fibrous  tissue  which  is  attached  to  a 
muscle. 

Arach'noid.  Resembling  a  web.  The  middle  of  the  three  membranes  of 
the  brain  and  spinal  cord. 

Arboriza'tion.  A  branching  distribution  of  veinlets  or  of  nerve-filaments, 
especially  the  branched  terminal  ramifications  of  a  nerve-axone. 

Are'olar.  That  form  of  connective  tissue  which  fills  the  interstices  be- 
tween the  various  parts  of  the  body ;  cellular. 

Asex'ual.  Having  no  distinction  of  sex;  having  no  relation  to  sex. 
Asexual  reproduction,  reproduction  without  sexual  intercourse. 

Asphyx'ia.     Suspended  animation. 

Assimila'tion.     The  conversion  of  food  into  living  tissue. 

At'las.  The  first  cervical  vertebra  by  which  the  head  articulates  with 
the  spinal  column,  so  called  because  it  supports  the  head  as  Atlas 
was  fabled  to  support  the  world  on  his  shoulders. 

At'rophy.     Wasting  of  a  part  from  lack  of  nutrition. 

Au'ditory.     Pertaining  to  the  sense  or  organ  of  hearing. 

Augmenta'tion.    The  act  of  increasing  or  making  larger. 

Aur'icle.  A  term  applied  to  the  ear-shaped  cavities  of  the  heart,  also  to 
the  expanded  portion  of  the  external  ear. 

Automatic.  Performed  without  the  will;  spontaneous.  Same  as  au- 
tonomic. 

Autonom'ic.  Performed  without  the  will;  spontaneous.  Same  as  au- 
tomatic. 

Auton'omy.  Independence ;  the  condition  of  having  independent  func- 
tions, limitations,  and  laws. 

Ax'is.    The  second  cervical  or  odontoid  vertebra.     Same  as  epistropheus. 

Az'ygos.    Without  a  fellow ;  hence,  unpaired,  single. 

Bi'fid.     Cleft  in  the  middle. 

Bifurcation.     Division  into  two  branches  or  forks. 


GLOSSARY  493 

Blas'toderm.    The  primitive  membrane  or  layer  of  cells  resulting  from  the 

subdivision  of  the  germ. 
Brach'ial.     Belonging  to  the  arm. 
Brach'io-cephal'ic.     Of  or  pertaining  to  both  the  upper  arm  and  head; 

as  the  brachio-cephalic  (innominate)  artery  and  veins. 
Bron'chiole.     A  small  bronchial  tube. 

Bron'chus,  pi.  Bron'chi.     One  of  the  two  main  branches  of  the  trachea. 
Buc'cal.     Pertaining  to  the  mouth  or  cheeks. 
Buc'cinator.    The  trumpeter's  muscle.    A  thin,  flat  muscle  that  helps  to 

form  the  wall  of  the  cheek. 

Bur'sal.     Pertaining  to  bursts,  membranous  sacs. 
But'tock.     The  part  at  the  back  of  the  hip  which,  in  man,  forms  one  of 

the  protuberances  on  which  he  sits. 
Butyr'ic  Acid.    A  colorless  liquid  having  a  strong  rancid  smell  and  acrid 

taste.    C3H7COOH. 

Cae'cum.    The  first  portion  of  the  large  intestine  —  a  blind  pouch. 

CaTculus,  pi.  CaTculi.     A  stone. 

Calyx,  pi.  Cal'yces.     Small  cup-like  membranous  canals,  which  surround 

the  papillae  of  the  kidney,  and  open  into  its  pelvis. 
Canalic'ulus,  pi.  Canalic'uli.     A  small  channel,  or  vessel. 
Cancellated.     A  term  used  to  describe  the  lattice-work  texture  of  bone. 
Ca'nine.     Pointed  like  the  tusks  of  a  dog.     Name  given  to  the  third  tooth 

on  each  side  of  the  jaw. 
Can'thus.    The  angle  formed  by  the  junction  of  the  eyelids,  the  internal 

being  the  greater,  the  external  the  lesser,  canthus. 
Car'dio-inhib'itory.     An  agent  which  restrains  the  heart's  action. 
Car'pus.     The  assemblage  of  bones  forming  the  wrist. 
Car'tilage.    A  solid  but  flexible  material,  forming  a  part  of  the  joints, 

air-passages,  nostrils,  etc.    Gristle. 
Casein'ogen.     The  curd  separated  from  milk  by  the  addition  of  rennet, 

constituting  the  basis  of  cheese. 
Cau'da  Equi'na.     A  term  applied  to  the  termination  of  the  spinal  cord, 

which  gives  off  a  large  number  of  nerves  which,  when  unravelled,  re- 
semble a  Worse's  tail. 
Cau'date.     Tail-like. 

Centrifugal.     Flying  off  or  proceeding  from  the  centre.    Same  as  efferent. 
Centrip'etal.    Tending  or  moving  toward  the  centre.     Same  as  afferent. 

Opposed  to  centrifugal. 


494  GLOSSARY 

Cen'trosome.  A  peculiar  rounded  body  lying  near  the  nucleus  of  the  cell. 
It  is  regarded  as  the  dynamic  element  by  means  of  which  the  machin- 
ery of  cell  division  is  organized. 

Cephal'ic.     Pertaining  to  the  head. 

Chi' asm.  A  crossing  or  decussation ;  especially  that  of  the  fibres  of  the 
optic  nerve. 

Choles'terin.  A  tasteless,  inodorous,  fatty  substance  found  in  small 
quantities  in  the  protoplasm  of  all  cells,  especially  in  nerve-tissue, 
blood  cells,  and  bile. 

Chon'drin.     A  kind  of  gelatin  obtained  by  boiling  cartilage. 

Chor'dae  Tendin'eae.     Tendinous  cords. 

Chor'da  Tym'pani.  The  tympanic  cord,  a  branch  of  the  facial,  or  seventh 
cranial  nerve,  which  traverses  the  tympanic  cavity  and  joins  the 
gustatory,  or  lingual,  nerve. 

Chro'mosome.  Any  one  of  the  chromatin  rods  into  which  the  spirem 
breaks  during  mitosis. 

Cica'trix.     The  mark,  or  scar,  left  after  the  healing  of  a  wound. 

Cil'ia.     Hair-like  processes  of  certain  cells. 

Coalesce'.     To  grow  together. 

Cce'liac.     Pertaining  to  the  abdominal  cavity. 

Collaterals.     Situated  at  the  side ;  hence,  also  secondary. 

Colum'nae  Car'neae.  "  Fleshy  columns ;  "  muscular  projections  in  the 
ventricles  of  the  heart. 

Com'missure.  A  joining  or  uniting  together.  Something  which  joins 
together. 

Congenital.     Born  with  a  person,  existing  from  or  before  birth. 

Contiguous.     Adjacent;  near;   in  actual  contact. 

Convec'tion.  A  process  of  transfer  or  transmission,  as  of  heat  or  elec- 
tricity. The  term  "  convection  currents  "  is  used  in  the  text,  and 
applies  to  currents  of  air  produced  by  differences  in  temperature 
and  density.  Warm  air  expands,  becomes  less  dense,  and  is  forced 
upward  by  the  cooler  air,  which  is  heavier,  and  sinks  down.  In  this 
way  convection  currents  are  established. 

Convolu'tions.     The  tortuous  foldings  of  the  external  surface  of  the  brain. 

Co'rium.     The  deep  layer  of  the  skin ;  the  derma. 

Cor'onary.  A  term  applied  to  vessels,  ligaments,  and  nerves  which  en- 
circle parts  like  a  crown,  as  the  coronary  arteries  of  the  heart. 

Cor'pus  Callo'sum.  A  name  given  to  the  white  medullary  substance  join- 
ing the  cerebral  hemispheres. 


GLOSSARY  495 

Cor'pus  Lu'teum.    Yellow  body,  in  the  ovary  taking  the  place  of  a  Graafian 

follicle  which  has  discharged  its  ovum. 
Correla'tion.     The  interdependence  of  organs  or  functions ;  the  reciprocal 

relations  of  organs. 
Cor'tex.     External  or  surface  layer  of  an  organ,  such  as  the  kidney  or 

brain. 

Cos'tal.     Pertaining  to  the  ribs. 
Crena'ted.     Notched  on  the  edge. 
Crib'riform.     Perforated  like  a  sieve. 
Cru'ra  Cer'ebri.     Pillars  of  the  cerebrum. 
Crypt.     A  secreting  cavity ;  a  follicle,  or  glandular  cavity. 
Cul-de-sac.     A  tube  or  cavity  closed  at  one  end. 

Cu'ticle.     A  term  applied  to  the  upper,  or  epidermal,  layer  of  the  skin. 
Cu'tis  Ve'ra.     The  true  skin ;  that  underneath  the  epidermal  layer. 
Cys'tic.     Pertaining  to  a  cyst,  —  a  bladder  or  sac. 

Decomposi'tion.  (1)  The  separation  of  compound  bodies  into  their  con- 
stituent parts  or  principles.  (2)  Any  ordinary  process  of  decay, 
especially  putrefaction. 

Decussa'tion.     To  cross  in  the  form  of  the  letter  X. 

Degluti'tion.     The  act  or  power  of  swallowing. 

Del'toid.   Having  a  triangular  shape ;  resembling  the  Greek  letter  A  (delta) . 

Den'drite.  A  branching,  protoplasmic  process  of  a  nerve-cell.  Same  as 
dendrone. 

Denti'tion.  (1)  The  process  of  cutting  teeth.  (2)  The  time  during  which 
teeth  are  being  cut.  (3)  The  kind,  number,  and  arrangement  of 
teeth  proper  to  any  animal. 

Diabe'tes  Insip'idus.  A  rare  disease  characterized  by  chronic  polyuria, 
the  urine  having  a  low  specific  gravity,  and  being  free  from  sugar. 

Diabe'tes  Melli'tus.  A  morbid  chronic  polyuria,  associated  with  thirst 
and  often  with  wasting,  and  with  the  presence  of  abnormal  con- 
stituents (sugar)  in  the  urine. 

DiaTysis.  The  passage  through  a  permeable  membrane  of  a  substance  in 
solution. 

Diapede'sis.  Passing  of  the  red  blood  cells  through  vessel  walls  without 
rupture. 

Dias'tole.     The  dilatation  of  the  heart. 

Diath'esis.  A  congenital  condition  of  the  system  which  renders  it  pecul- 
iarly liable  to  some  diseases. 


496  GLOSSARY 

Dichot'omous.  Divided  into  two.  Pertaining  to  or  consisting  of  a  pair 
or  pairs. 

Dicrot'ic.  Applied  to  the  pulse,  when  there  is  a  rebounding,  like  a  double 
pulsation ;  having  a  double  beat. 

Diffu'sion.  A  property  of  certain  bodies  of  dispersing  or  mixing  them- 
selves with  the  surrounding  medium. 

Diplog.    The  osseous  tissue  between  the  tables  of  the  skull. 

Dis'cus  Prolig'erus  or  germ  disc.  A  term  applied  to  a  mass  of  cells 
clinging  to  the  ovum  when  it  is  set  free  from  the  ovary.  More  recent 
term  is  "  ovarian  mound." 

Disintegration.     A  breaking  apart. 

Distilla'tion.  The  act  of  distilling  or  of  falling  in  drops.  The  operation 
of  driving  off  gas  or  vapor  from  volatile  liquids  or  solids,  by  heat  in  a 
retort  or  still,  and  the  condensation  of  the  products  as  far  as  possible 
by  a  cooler  receiver. 

Dor'sal.     Pertaining  to  the  back,  or  posterior  part,  of  an  organ. 

Du'ra  Ma'ter.  The  outer  membrane  of  the  brain  and  spinal  cord.  The 
"hard  mother,"  called  dura  because  of  its  great  resistance,  and  mater 
because  it  is  the  guardian  or  protector  of  the  brain. 

Ec'toderm.    The  completed  outer  layer  of  cells,  or  outer  blastodermic 

membrane.     Same  as  epiblast. 
Ectop'ic.     Characterized  as  being  out  of  place. 
Ectop'ic  Gesta'tion.    The  name  given  to  pregnancy,  when  the  fecundated 

ovum,  instead  of  entering  the  uterus,  either  remains  in  a  Fallopian 

tube,  or  the  abdominal  cavity. 
Efferent.     Bearing   or  carrying  outwards,   as   from  the  centre  to  the 

periphery. 

Elemen'tary.     Pertaining  to  or  of  the  nature  of  an  element  or  elements. 
Elimina'tion.     The  act  of  expelling  waste  matters. 
Em'bolus.    A  portion  of  a  blood  clot  which  has  been  formed  in  one  of  the 

larger  vessels,  and  has  afterward  been  forced  into  one  of  the  smaller 

vessels,  where  it  may  act  as  a  wedge. 
Em'bryo.     The  ovum  and  product  of  conception  up  to  the  fourth  month, 

when  it  becomes  known  as  the  foetus. 
Empir'ical.     Relating  to  a  knowledge  of  medicine  obtained  by  experience 

alone. 

Endocar'dium.     Lining  of  the  heart. 
Endogenous.    Originating  within  the  organism ;  not  exogenous. 


GLOSSARY  497 

En'dolymph.    The  fluid  in  the  membranous  labyrinth  of  the  ear. 

Endos'teum.  The  lining  membrane  of  the  medullary  cavity  of  a  bone; 
the  internal  periosteum. 

Endothe'lium.  A  term  applied  to  single  layers  of  flattened  transparent 
cells,  applied  to  each  other  at  their  edges  and  lining  certain  surfaces 
and  cavities  of  the  body.  In  contradistinction  to  epithelium. 

En'siform.     Shaped  like  a  sword. 

En'toderm.  The  completed  inner  layer  of  cells,  or  inner  blastodermic 
membrane.  Opposed  to  ectoderm.  Same  as  hypoblast. 

Epicra'nial.     That  which  is  upon  the  cranium  or  scalp. 

Epider'mis.     The  outer  layer  of  the  skin. 

Epigas'tric.  Lying  upon,  distributed  over,  or  pertaining  to  the  abdomen 
or  the  stomach. 

Epiglot'tis.  The  cartilage  at  the  root  of  the  tongue  which  forms  a  lid  or 
cover  for  the  aperture  of  the  larynx. 

Epimys'ium.  The  sheath  of  connective  tissue  surrounding  an  entire 
muscle. 

Equilibrium.  That  condition  of  rest  which  results  when  all  the  forces 
acting  in  a  body  are  equally  opposed.  In  physiology  it  signifies  the 
harmonious  action  of  the  organs  of  the  body,  as  in  standing. 

Evaporation.  The  act  of  resolving  into  vapor.  In  order  to  produce 
vapor,  heat  is  necessary  and,  if  not  supplied,  is  taken  from  near  ob- 
jects. Thus  the  heat  necessary  for  the  evaporation  of  perspiration 
is  taken  from  the  body. 

Excre'tion.  The  separation  from  the  blood  of  waste  particles ;  also  the 
materials  excreted. 

Exog'enous.     Developed  outside  of  the  body. 

Exuda'tion.  The  passing  out  of  any  liquid  through  the  walls  or  mem- 
branes of  the  vessels  containing  it. 

FaTciform.     Sickle-shaped. 

Fallo'pian.     A  term  applied  to  tubes  and  ligaments  first  pointed  out  by 

the  anatomist  Fallopius. 

Fascic'ulus,  pi.  Fascic'uli.     A  bundle  of  close-set  fibres. 
Fau'ces.    The  constricted  passage  at  the  back  of  the  mouth  connecting 

the  oral  cavity  and  the  pharynx. 

Fecunda'tion.     The  act  of  making  fruitful  or  prolific.     Impregnation. 
Fenes'tra.     A  window. 
Fibril'la,  pi.  Fibrillae.     A  little  fibre. 

2K 


498  GLOSSARY 

Fi'brous.  Containing  or  consisting  of  fibres.  Having  the  character  of 
fibres. 

Fil'iform.     Thread-like. 

Fim'bria,  pi.  Fim'briae.     A  border,  or  fringe. 

Fis'sion.    A  cleaving,  or  breaking  up  into  two  parts. 

Flat'ulence.    Undue  generation  of  gases  in  the  stomach  and  intestines. 

Fo'cus.  A  point  at  which  the  rays  of  light  meet  after  being  reflected  or 
refracted.  Point  at  which  an  image  is  formed. 

Fce'tus.     The  child  in  utero  from  the  fourth  month  of  pregnancy  till  birth. 

Follicle.     A  little  bag;  a  small  gland. 

Fontanelle'.  A  term  applied  to  the  membranous  spaces  existing  between 
the  cranial  bones  in  the  new-born  infant.  In  these  spaces  the  pulsa- 
tion of  the  blood  in  the  cranial  arteries  was  imagined  to  rise  and  fall 
like  the  water  in  a  fountain. 

Fora'men,  pi.  Foram'ina.     An  opening,  hole,  or  aperture. 

Fos'sa,  pi.  Fos'sae.     A  depression,  or  sinus ;  literally,  a  ditch. 

Fo'vea  Centralis.  Central  depression  of  the  macula  lutea.  The  point 
of  most  acute  vision. 

Fun'dus.  The  base  or  closed  part  of  any  organ  which  has  an  external 
opening. 

Fun'giform.     Having  the  shape  of  a  mushroom. 

Funic'ulus,  pi.  Funic'uli.     A  little  cord,  or  bundle,  of  aggregated  fibres. 

Fu'siform.     Spindle-shaped. 

Gan'glion,  pi.  Gan'glia.     A  collection  of  nerve-cells  in  the  course  of  a 

nerve,  having  the  appearance  of  a  knot. 
Generative.     Pertaining  to  generation,  or  propagation.     Connected  with 

or  resulting  from  the  process  of  begetting. 
Gen'itals.     Pertaining  to  the  organs  of  generation. 
Gen'ito-u'rinary.     Relating  to  the  genital  and  urinary  organs. 
Gesta'tion.     The  act  or  condition  of  carrying  young  in  the  womb  from 

conception  to  delivery.     Pregnancy. 
Glair'y.     Like  the  clear  white  part  of  an  egg. 
Gle'noid.     A  name  given  to  a  shallow  cavity. 
Glob'ulins.     Protein  substances  somewhat  similar  to  the  albumins,  but 

differing  in  their  solubility. 
Glomer'ulus.     A  botanical  term  signifying  a  small,  dense,  roundish  cluster : 

a  term  applied  to  the  ball-like  tuft  of  vessels  in  the  cortical  portion 

of  the  kidneys. 


GLOSSARY  499 

Glute'i,  pi.  of  Glute'us.     The  muscles  forming  the  buttocks. 

Gly'cogenolysis.     Conversion  of  glycogen  into  glucose. 

Glycosu'ria.     The  presence  of  sugar  in  the  urine. 

Graaf'ian  Follicles,  or  Ves'icles.  A  term  applied  to  the  sacs  in  the  ova- 
ries, which  contain  the  ova,  or  cells. 

Granula'tions.  Grain-like,  fleshy  bodies  that  form  on  the  surface  of 
wounds  and  ulcers. 

Gus'tatory.    Belonging  to  the  sense  of  taste. 

Haemoglo'bin.  A  compound  protein  found  in  the  red  cells  of  the  blood ; 
its  molecule  consists  of  a  protein  portion  and  of  a  pigment  portion,  the 
latter  containing  one  atom  of  iron. 

Hsemorrhoi'dal.  Pertaining  to  haemorrhoids,  small  tumors  of  the  rectum, 
which  frequently  bleed. 

Hem'atin.  A  proteid-free,  pigmented  constituent  of  haemoglobin  ob- 
tained by  treating  with  acids. 

Hemol'ysis.  Destruction  of  the  red  blood-cells  with  a  setting  free  of  the 
haemoglobin. 

Hemophil'ia.  A  congenital,  morbid  condition,  characterized  by  a  tend- 
ency to  bleed  immoderately  from  any  insignificant  wound,  or  even 
spontaneously. 

Hi'lum,  sometimes  written  Hi'lus.  It  is  the  depression,  usually  on  the 
concave  side  of  a  gland,  where  vessels,  nerves,  and  ducts  enter  or  leave. 

Histol'ogy.  That  branch  of  anatomy  which  is  concerned  with  the  micro- 
scopic structure  of  the  tissues  of  the  body. 

Homoge'neous.  Of  the  same  kind  or  quality  throughout;  uniform  in 
nature,  —  the  reverse  of  heterogeneous. 

Homother'mous.  Of  equal  temperature.  Applied  to  animals  whose 
temperature  remains  practically  constant. 

Hor'mone.  A  substance  which  is  produced  in  one  organ,  and  on  being 
carried  by  the  blood  to  another  organ,  stimulates  this  latter  to  func- 
tional activity. 

Hy'aloid.  The  name  given  the  membrane  which  encloses  the  vitreous 
humor  of  the  eye. 

Hydrother'apy.  A  mode  of  treating  disease  by  the  copious  use  of  pure 
water,  both  internally  and  externally. 

Hyperglycae'mia.     An  abnormal  amount  of  sugar  in  the  blood. 

Hyper'trophy.  Excessive  growth;  thickening  or  enlargement  of  any 
part  or  organ. 


500  GLOSSARY 

Hypochon'driac.  A  term  applied  to  the  region  of  the  abdomen  under 
the  cartilages  of  the  false  ribs. 

Hypogas'tric.  Situated  below  the  stomach.  Pertaining  to  the  hypo- 
gastrium. 

Hypoglos'sal.    A  name  given  to  the  motor  nerve  of  the  tongue. 

Hypoph'ysis.  The  pituitary  body  of  the  brain  which  is  lodged  in  the  cen- 
tral depression  of  the  sphenoid  bone. 

Il'eum.     The  twisted  portion  of  the  small  intestine. 

ITium,  pi.  H'ia.     The  upper  part  of  the  os  innominatum. 

Immis'cible.     Not  capable  of  being  mixed. 

Inflamma'tion.     A  morbid  condition  characterized  by  pain,  heat,  redness, 

.    swelling,  and  usually  loss  of  function. 
Infundib'ulum,  pi.  Infundib'ula.     A  funnel-shaped  canal. 
Ingest'.    Taking  food  into  the  stomach. 
In'guinal.     Pertaining  to  the  groin. 
Inhibition.     Restraint;    the  physiological  arrest  or  suppression  of  any 

process,  effected  through  nerves  and  special  nerve  centres. 
Innom'inate.     A  name  given  an  artery,  a  vein,  and  a  bone. 
Inocula'tion.     The  injection  of  virus  into  any  part  of  the  body,  either  as 

an  operative  procedure  or  by  accident. 
Inos'culate.     To  unite,  to  open  into  each  other. 
In'sulate.    To  isolate  or  separate  from  surroundings. 
Integ'ument.     The  skin,  or  outer  covering,  of  the  body. 
Intercellular.     Lying  between  cells. 
Intercos'tal.     Situated  or  intervening  between  successive  ribs  of  the  same 

side  of  the  body. 

Interlob'ular.     That  which  lies  between  the  lobules  of  any  organ. 
In'terstice.     The  space  which  stands  between  things;    spaces  between 

parts. 

Inter sti'tial.     Pertaining  to  or  containing  interstices. 
Intes'tine.     The  part  of  the  alimentary  canal  which  is  continuous  with 

the  lower  end  of  the  stomach ;  also  called  the  bowels. 
Intralob'ular.     That  which  lies  within  the  lobules  of  any  organ. 
I'ris.     The  colored  membrane  suspended  behind  the  cornea  of  the  eye. 
Is'chium,  pi.  Is'chii.     The  lower  portion  of  the  os  innominatum ;  that  upon 

which  the  body  is  supported  in  a  sitting  posture. 

Jeju'num.  The  part  of  the  small  intestine  comprised  between  the  duo- 
denum and  ileum. 


GLOSSARY  501 

Katab'olism.  The  process  by  means  of  which  complex  substances  are 
rendered  more  simple  and  less  complex.  The  opposite  of  anabolism. 

Lacta'tion.     The  period  of  giving  milk. 

Lactiferous.     Bearing,  or  conveying  milk,  as  a  lactiferous  duct. 

Lacu'na,  pi.  Lacu'nae.     A  little  hollow  space. 

Lambdoi'dal.     Resembling  the  Greek  letter  A. 

Lameria,  pi.  Lamellae.     A  thin  plate,  or  layer. 

Lam'ina.     A  thin  plate ;  a  germinal  layer. 

Laryn'goscope.  The  instrument  by  which  the  larynx  may  be  examined 
in  the  living  subject. 

Lar'ynx.  The  upper  part  of  the  air-passage,  between  the  trachea  and  the 
base  of  the  tongue. 

Latis'simus  Dor'si.     The  widest  muscle  of  the  back. 

Lens.  A  transparent  substance,  usually  glass,  bounded  by  two  curved 
surfaces,  or  by  one  curved  and  one  plain.  There  are  two  general 
classes  of  lenses :  (1)  concave,  which  are  thinner  at  the  centre  than  at 
the  edges ;  and  (2)  convex,  which  are  thicker  at  the  centre  than  at 
the  edges.  (See  page  454.) 

Lob'ule.     A  small  lobe. 

Lum'bar.     Pertaining  to  the  loins. 

Lu'men.    The  transverse  section  of  a  vessel  or  cavity.  , 

Lym'phoid.     Having  resemblance  to  lymph. 

Mac'ula  Lu'tea.     Yellow  spot. 

Malle'olus,  pi.  Malle'oli.     A  name  given  to  the  pointed  projections  formed 

by  the  bones  of  the  leg  at  the  ankle-joint. 
Malpi'ghian  Bodies  (so  called  in  honor  of  Malpighi,  a  celebrated  Italian 

anatomist).     A  term  applied  to  small  bodies,  or  corpuscles,  found  in 

the  kidney  and  spleen. 

Ma'trix.     The  womb.     Producing  or  containing  substance. 
Matura'tion.     The  process  of  bringing,  or  of  coming  to  maturity. 
Mea'tus.     An  opening  leading  to  a  canal,  duct,  or  cavity. 
Mediasti'num.     The  septum  of  the  pleura  which  divides  the  cavity  of  the 

thorax  into  two  parts. 

^ 

Medulla  Oblonga'ta.  That  portion  of  the  brain  which  lies  within  the 
skull,  upon  the  basilar  process  of  the  occipital  bone. 

Meibo'mian.  A  term  applied  to  the  small  glands  between  the  conjunc- 
tiva and  tarsal  cartilages,  discovered  by  Meibomius.  More  recent 
term  is  tarsal  glands. 


502  GLOSSARY 

Mes'entery.    A  fold  of  peritoneum  attaching  some  part  of  the  intestine 

to  the  posterior  wall  of  the  abdomen. 
Me'sial.     Median,  dividing  into  two  symmetrical  portions. 
Mesocolon.     A  duplicature  of  the  peritoneum  covering  the  colon. 
Metab'olism.     The  changes  taking  place  in  cells,  whereby  they  become 

more  complex  and  contain  more  force,  or  less  complex  and  contain 

less  force.    The  former  is  constructive  metabolism,  or  anabolism; 

the  latter,  destructive  metabolism,  or  katabolism. 
Metacar'pus.     The  part  of  the  hand  comprised  between  the  wrist  and 

fingers. 
Metatar'sus.     That  part  of  the  foot  comprised  between  the  instep  and 

toes. 

Mito'sis.     Processes  of  indirect  cell-division.     Same  as  karyokinesis. 
Mi'tral.     Resembling  a  mitre. 
Mu'cin.     The  chief  constituent  of  mucus. 
Myocar'dium.     The  muscular  structure  of  the  heart. 
My'osin.     Chief  protein  substance  of  muscle. 

Na'ris,  pi.  Na'res.     A  nostril. 

Neurilem'ma.     Nerve-sheath. 

Neurog'lia.  The  supporting  tissue  of  the  nervous  system,  contains  the 
glia  cells. 

Neu'rone.     The  nerve-cell,  inclusive  of  all  its  processes. 

Node.     A  lymphatic  ganglion. 

Nucle'olus,  pi.  Nucle'oli.     A  smaller  nucleus  within  the  nucleus. 

Nu'cleus,  pi.  Nu'clei.     A  minute  vesicle  embedded  hi  the  cell  protoplasm. 

Nutri'tion.  The  processes  by  which  the  nourishment  of  the  body  is  ac- 
complished. 

Odon'toid.     Tooth-like. 

(Ede'ma.     A  swelling  from  effusion  of  serous  fluid  into  the  areolar  tissue. 

Or'bital.     Pertaining  to  the  orbit,  the  bony  cavity  in  which  the  eyeball  is 

suspended. 

Or'gan.    Any  part  of  the  body  with  a  special  function. 
Or'ifice.    An  opening. 
Os,  pi.  O'ra.     A  mouth. 
Os,  pi.  Os'sa.     A  bone. 

Oscilla'tion.     Swinging  backward  and  forward ;   vibration. 
Os  Cox'a,  pi.  Os'sa  Cox'se.     The  hip  bone,  or  os  innominatum. 


GLOSSARY  503 

Os'sa  Innomina'ta,  pi.  of  Os  Innomina'tum.  "  Unnamed  bones."  The 
irregular  bones  of  the  pelvis,  unnamed  on  account  of  their  non-resem- 
blance to  any  known  object. 

Os'seous.     Consisting  of  or  resembling  bone. 

Os'sicle.    A  small  bone. 

Os'teoblasts.    The  germinal  cells  deposited  in  the  development  of  bone. 

O'toliths.  Particles  of  calcium  carbonate  and  phosphate  found  in  the 
internal  ear. 

O'vum,  pi.  O'va.    The  human  germ-cell. 

Pal'ate.    The  roof  of  the  mouth,  consisting  of  the  hard  and  soft  palate. 

Pan'creas.  A  compound  secreting  gland;  one  of  the  accessory  organs 
of  nutrition.  The  sweetbread  of  animals. 

Papillae,  pi.  of  Papilla.  Minute  eminences  on  various  surfaces  of  the 
body. 

Pari'etal.     Pertaining  to  a  wall. 

Parturi'tion.     The  act  of  giving  birth  to  young. 

Pec'toral.     Pertaining  to  the  breast,  or  chest. 

Ped'icle.     A  stalk. 

Pedun'cle.     A  narrow  part  acting  as  a  support. 

Per'meable.  Capable  of  being  passed  through ;  substances  which  allow 
the  passage  of  fluids. 

Perone'al.  Pertaining  to  the  fibula;  a  term  applied  to  muscles,  or  vessels, 
in  relation  to  the  fibula. 

Pe'trous.     Having  the  hardness  of  rock. 

Phalan'ges.  A  name  given  to  the  small  bones  forming  the  fingers  and 
toes,  because  placed  alongside  one  another  like  a  phalanx. 

Phar'ynx.     The  cavity  forming  the  upper  part  of  the  gullet. 

Phlebot'omy.     The  opening  of  a  vein ;  venesection. 

Phona'tion.     Utterance  of  vocal  sounds. 

Phren'ic.     Pertaining  to  the  diaphragm. 

Pi'a  Ma'ter.    The  most  internal  of  the  three  membranes  of  the  brain. 

Pig'ment.     Coloring  matter. 

Pis'iform.    Having  the  form  of  a  pea.     One  of  the  carpal  bones. 

Placen'ta.  Aflat,  circular,  vascular  body  which  forms  the  organ  of  nutri- 
tion and  excretion  for  the  foetus  in  utero. 

Plan'tar.     Pertaining  to  the  sole  of  the  foot. 

Plex'us.     A  network  of  nerves  or  veins. 

Pneumogas'tric.     Pertaining  to  the  lungs  and  stomach. 


504  GLOSSARY 

Poi'kilother'mous.  Changing  the  body  temperature  with  the  temperature 
of  the  surrounding  medium ;  applied  to  cold-blooded  animals,  bacteria, 
and  plants.  The  human  foetus  is  cold-blooded. 

Polyu'ria.     Excessive  flow  of  watery  urine. 

Pons  Varolii.  "  Bridge  of  Varo'lius."  The  square  portion  of  medullary 
substance  connecting  the  cerebrum,  cerebellum,  and  medulla  oblon- 


Poplite'al.    The  space  behind  the  knee-joint  is  called  the  popliteal  space. 

Prismat'ic.  Resembling  a  prism,  which,  in  optics,  is  a  solid,  triangular- 
shaped  glass  body. 

Prona'tion.     The  turning  of  the  hand  with  the  palm  downward. 

Prona'tor.     The  group  of  muscles  which  turn  the  hand  palm  downward. 

Pseudopo'dium.  A  protrusion  of  the  substance  of  an  amoeba  or  an  amoe- 
boid cell,  as  in  locomotion. 

Psy'chical.     Pertaining  to  the  mind. 

Pu'berty.  Sexual  maturity  in  the  human  race ;  the  age  at  which  repro- 
duction becomes  possible. 

Pu'bis,  pi.  Pu'bes.  The  hairy  region  above  the  genitals,  also  used  for  os 
pubis,  the  portion  of  the  os  innominatum  forming  the  front  of  the 
pelvis. 

Pyrex'ia.     Elevation  of  temperature ;  fever. 

Radia'tion.  The  act  of  spreading  outward  from  a  central  point.  The 
diffusion  of  rays  of  light. 

Rale.  A  rattling,  bubbling  sound  attending  the  circulation  of  air  in  the 
lungs.  Different  from  the  murmur  produced  in  health. 

Rec'tus,  pi.  Rec'ti.  Straight.  A  name  given  to  muscles  of  the  eye  and 
abdomen. 

Reflec'tion.  The  return  of  rays,  beams,  sound,  or  the  like  from  a  surface. 
Reflection  of  light  is  of  two  kinds,  regular  and  diffused.  When  a  beam 
of  light  enters  a  darkened  room  through  a  small  opening  and  strikes 
a  mirror,  a  reflected  beam  will  be  seen  travelling  along  some  definite 
path.  This  is  called  regular  reflection.  Should  the  light,  however, 
fall  on  a  piece  of  white  paper,  it  would  be  reflected  and  scattered  in 
all  directions.  This  is  called  diffused  reflection,  and  is  caused  by  the 
inequalities  of  the  reflecting  surface.  All  rough  surfaces,  as  well  as 
dust  and  moisture  in  the  atmosphere,  serve  to  diffuse  light.  If  this 
were  not  the  case,  it  would  be  dark  everywhere  except  in  the  direct 
path  of  light  from  some  luminous  body. 


GLOSSARY 


505 


^^ 


Refrac'tion.  The  bending  or  deviation  in  the  course  of  rays  of  light  in 
passing  obliquely  from  one  transparent  medium  into  another  of  dif- 
ferent density.  Light  waves  travel  with  different  velocities  in 
mediums  of  different  densities,  the  more  dense  the  medium,  the  less 
the  velocity.  For  in- 
stance, light  will  travel  /(\ 
less  rapidly  in  water  than 
in  air.  For  this  reason 
where  a  ray  of  light  in 
air  strikes  a  body  of 
water  obliquely,  it  will 
be  bent  out  of  a  straight 
line,  as  shown  in  the 
following  diagram;  the 
light  ray  AC,  instead  of 
following  the  straight 
line  AB,  is  bent  on  strik- 
ing the  surface  of  the 
dense  medium,  thereby 
being  bent  from  its  direct 
path  toward  C. 

Resiliency.     The  act  of  leaping,  or  springing  back ;  the  act  of  rebounding. 

Res'tiform.     In  anatomy  denoting  a  part  of  the  medulla  oblongata,  called 
the  restiform  body. 

Retic'ular.     Resembling  a  small  net. 

Ret'if orm.     Having  the  form,  or  structure,  of  a  net. 

Ret'ina.     The  most  internal  membrane  of  the  eye ;  the  expansion  of  the 
optic  nerve. 

Ru'gae.     A  term  applied  to  the  folds,  or  wrinkles,  in  the  mucous  membrane, 
especially  of  the  stomach  and  vagina. 

Sag'ittal.     Arrow-like. 

Saliva'tion.    An  excessive  secretion  of  saliva. 

Saphe'nous.    A  name  given  to  the  two  large  superficial  veins  of  the  lower 

limbs. 

Sap 'id.     Possessing  savor  or  flavor. 
Saponifica'tion.     Conversion  into  soap. 
Se'bum,  or  Se'vum.     A  fatty  secretion  resembling  suet,  which  lubricates 

the  surface  of  the  skin. 


jfcr- 


506  GLOSSARY 

Secre'tion.     The  process  of  separating  from  the  blood  some  essential 

fluid,  which  fluid  is  also  called  a  secretion. 
Secre'togogue.     An  agent  which  stimulates  secretion. 
Segmenta'tion.    The  process  of  division  of  the  fertilized  ovum  before 

differentiation  into  layers  occurs. 
Se'rum.    The  clear  liquid  which  separates  in  the  clotting  of  blood  from 

the  clot  and  blood  cells. 
Ses'amoid.     Resembling  a  grain  of  sesamum.     A  term  applied  to  the 

small   bones  situated  in  the    substance  of   tendons,  near  certain 

joints. 

Sig'moid.     Curved  like  the  letter  s. 

Soleus.    A  name  given  to  a  muscle  shaped  like  the  sole  of  a  shoe. 
Sphinc'ter.    A  circular  muscle  which  contracts  the  aperture  to  which  it 

is  attached. 

Splanch'nic.     Of  or  pertaining  to  the  viscera. 
Squa'mous.     Scale-like. 
Sta'sis.     Stagnation  of  the  blood  current. 
Stim'ulus,  pi.  Stim'uli.     Anything  that  excites  to  action. 
Sto'ma,  pi.  Sto'mata.    A  mouth;  a  small  opening. 
Strat'ified.     Formed  or  composed  of  strata,  or  layers. 
Stri'ated.     That  which  has  stria,  furrows,  or  lines. 
Stro'ma.     The  foundation  or  bed  tissue  of  an  organ. 
Styloid.    A  long  and  slender  process  from  the  lower  side  of  the  temporal 

bone. 

Sudoriferous.     A  term  applied  to  the  glands  secreting  sweat. 
Sul'cus.    A  fissure  between  two  convolutions   of  the  surface  of  the 

brain. 

Supina'tion.     The  turning  of  the  hand  with  the  palm  upward. 
Su'pinators.     The  muscles  which  turn  the  hand  with  the  palm  upward. 
Su'pra-or'bital.     Above  the  orbit. 
Su'ture.    That  which  is  sewn  together,  a  seam ;  the  seam  uniting  bones  of 

the  skull. 

Synap'se.     Interlacing  of  terminal  arborization  of  nerves. 
Sys'tole.     The  contraction  of  the  heart. 

Tac'tile.     Relating  to  the  sense  of  touch. 
Tar'sus.    The  instep ;  also  the  cartilage  of  the  eyelid. 
Tem'poral.     Pertaining  to  the  temples ;  the  name  of  an  artery  and  of  a 
bone. 


GLOSSARY  507 

Ten'do  Achillis.  "  Tendon  of  Achilles."  The  tendon  attached  to  the 
heel,  so  named  because  Achilles  is  supposed  to  have  been  held  by  the 
heel  when  his  mother  dipped  him  in  the  river  Styx  to  render  him  in- 
vulnerable. 

Ten'don.  The  white,  fibrous  cord,  or  band,  by  which  a  muscle  is  attached 
to  a  bone ;  a  sinew. 

Throm'bus.     Name  given  to  a  clot  formed  in  a  blood-vessel. 

Tibia'lis  Ante'rior.    The  muscle  situated  at  the  anterior  part  of  the  tibia. 

Tox'ic.     Poisonous. 

Trabec'ulae.  A  term  applied  to  prolongations  of  fibrous  membranes 
which  form  septa,  or  partitions. 

Transversa'lis.  A  term  applied  to  a  muscle  which  runs  in  a  transverse 
direction. 

Trape'zius.  A  name  given  to  the  two  upper  superficial  muscles  of  the 
back,  because  together  they  resemble  a  trapezium,  or  diamond-shaped 
quadrangle. 

Trap'ezoid.  One  of  the  bones  of  the  wrist.  The  second  one  of  the  distal 
row  on  the  radial  or  thumb  side. 

Tri'ceps.  A  term  applied  to  a  muscle  having  a  triple  origin,  or  three 
heads. 

Tricus'pid.     Having  three  points. 

Trigem'inal.    Threefold ;  triple ;  also  relating  to  the  fifth  nerve. 

Tu'bular.     Having  the  form  of  a  tube,  or  pipe. 

Umbili'cus.     A  round  cicatrix,  or  scar,  in  the  median  line  of  the  abdomen. 
Unicellular.     Composed  of  a  single  cell. 

Va'gus.     Pneumogastric  nerve. 

Vas'cular.     Relating  to  vessels ;   full  of  vessels. 

Ver'miform.     Worm-shaped. 

Ver'nix  Caseo'sa.  The  fatty  varnish  found  on  the  new-born  infant,  which 
is  secreted  by  the  sebaceous  glands  of  the  skin. 

Ver'tebra,  pi.  Ver'tebrae.     The  bones  of  the  spine. 

Vibra'tion.     The  act  of  moving  rapidly  to  and  fro. 

Villus,  pi.  Villi.  The  conical  projections  on  the  valvulse  conniventes, 
making  the  mucous  membrane  look  shaggy. 

Vit'reous.  Glass-like.  A  name  applied  to  the  transparent,  jelly-like 
substance  which  fills  the  back  part  of  the  eyeball  behind  the  crystal- 
line lens. 


508  GLOSSARY 

Vo'mer.    The  thin  plate  of  bone  shaped  somewhat  like  a  ploughshare 
which  separates  the  nostrils. 

Xi'phoid.     Shaped  like  or  resembling  a  sword,  ensiform. 

Zygomat'ic.    Of  or  pertaining  to  the  malar  bone,  or  this  bone  and  its  con- 
nections.    Constituting  or  entering  into  the  formation  of  the  zygome. 
Zy'mogen.    A  mother  substance  or  antecedent  of  an  enzyme. 


INDEX 


(And  see  Glossary,  pages  491  to  508.) 


Abdomen,  divisions  of,  279. 

muscles  of,  119,  136. 
action  of,  120. 

regions  of,  279. 
Abdominal  cavity,  18. 

ring,  external,  121. 
internal,  121. 

wall,  weak  places  in,  121. 
Abducens  nerve,  422. 
Abduction,  94. 
Absorption,  325,  333. 

paths  of,  325,  333. 
Accessory  thyroids,  344. 
Accommodation,  453,  462. 

conditions  affecting,  454,  462. 
Acetabulum,  83. 
Acetone,  in  urine,  370. 
Acid,  7. 

oxide,  7. 

Acromegaly,  347. 
Acromion  process,  80. 
Adam's  apple,  73,  252. 
Adduction,  94. 

Adductor  muscles  of  thigh,  127. 
Adenoid  tissue,  50. 
Adenoids,  278. 
Adipose  tissue,  48. 
Adolescence,  period  of,  472. 
Adrenal  bodies,  345,  353. 
Adrenalin,  345. 

Afferent  nerve-fibres,  34,  42,  132. 
Air,  complemental,  262. 

composition  of,  263. 

effect  of  respiration  upon  the,  263. 

expired,  263. 

inspired,  263. 

reserve,  262,  270. 

residual,  262,  270. 

tidal,  262,  270. 
Albumins,  161. 

as  food,  309. 

in  urine,  369. 
Albuminuria,  369. 
Alcohol,  341. 
Alexia,  420. 

Alimentary  canal,  271,  297. 
divisions  of,  272. 

system,  26,  41. 
Alkalies,  7. 
Alveoli  of  lungs,  255. 
Amino-acids,  161,  308. 
Amceba,  23. 


Amoeboid  movement,  23,  158. 
Amphiarthroses,  92,  96. 
Ampulla  of  semicircular  canals,  442. 
Amylase,  320. 
Anabolism,  23,  325. 
Anastomosis  of  arteries,  197,  198. 
Anatomical  position,  13. 
Anatomy,  definition  of,  13. 

divisions  of,  13. 
Anemia,  156. 
Annular  ligaments,  99. 
Anteflexion,  of  uterus,  467. 
Anteversion,  of  uterus,  467. 
Antibodies,  in  blood,  162,  171. 
Antigens,  in  blood,  162. 
Antithrombin,  163,  165. 
Antitoxins,  in  blood,  162. 
Antrum,  of  bone,  63. 

of  Highmore,  70. 
Anus,  289. 
Aorta,  201. 

abdominal,  203,  207,  225. 

arch  of,  202,  224. 

ascending,  202,  224. 

branches,  of,  203,  224. 

descending,  203. 

thoracic,  203,  206,  224. 
Aphasia,  420. 
Apnoea,  264. 
Aponeurosis,  46,  98. 
Appendix,  vermiform,  289. 
Aqueduct  of  Sylvius,  418. 
Aqueous  humor,  452,  462. 
Arachnoid,  141,  411. 
Arborizations,  end,  36. 

interepithelial,  36. 
Arch,  palmar,  206. 
Areas  of  brain,  419,  428. 
Areola,  45. 

of  mammary  gland,  474. 
Areolar  tissue,  44. 
Arm  bone,  80. 

Arrector  muscles  of  hairs,  380. 
Arterial  tone,  182. 
Arterioles,  183. 

Artery,  or  arteries,  173,  181,  194,  197, 
224. 

anastomosis  of,  197,  198. 

aorta,  201. 

axillary,  205. 

basilar,  204. 

blood  supply  of,  182. 
509 


510 


INDEX 


Artery,  or  arteries  —  continued 

brachial,  205. 

branches  of,  198. 

bronchial,  206. 

carotid,  common,  203. 
external,  204. 
internal,  204. 

coats  of,  181. 

cceliac  axis,  207. 

division  of,  198. 

distribution  of,  197. 

dorsal,  of  foot,  213. 

elasticity  of,  233. 

extensibility  of,  233. 

femoral,  210. 

gastric,  207. 

hemorrhoidal,  superior,  210. 

hepatic,  207,  295. 

hypogastric,  210. 

iliac,  common,  210,  225. 
external,  210. 
internal,  210. 

innominate,  203. 

inosculation  of,  198. 

intercostales,  207. 

lumbar,  210. 

mediastinal,  posterior,  207. 

mesenteric,  inferior,  209. 

superior,  208. 
-  nerve  supply  of,  182. 

ossophageal,  207. 

ovarian,  209. 

pericardial,  207. 

peroneal,  213. 

phrenic,  210. 

plantar,  external,  211. 
internal,  211.  ' 

plexus  of,  198. 

popliteal,  211. 

pulmonary,  199. 

radial,  206. 

renal,  208. 

sacral,  middle,  210. 

severed,  flow  of  blood  from,  235. 

sheath  of,  183. 

size  of,  183. 

spermatic,  208. 

splenic,  207,  348. 

structure  of,  181. 

subclavian,  205. 

suprarenal,  207. 

tibial,  anterior,  213. 
posterior,  211. 

tone  of,  182. 

ulnar,  206. 

uterine,  210. 
vertebral,  204. 
Arthrodia,  96. 

Articulations,  90 ;   and  see  Joints. 
Ascending    tracts    of   the    spinal    cord 

406. 

Asphyxia,  265. 
Association  areas  of  brain,  421,  428. 


Astigmatism,  454,  462. 
tlas,  75. 
torn,  3,  6. 

ttraction  sphere,  21. 
Auditory  apparatus,  437,  457. 
canal,  437,  457. 
nerve,  422,  442. 
Auricle  of  ear,  437,  457. 
Auricles  of  heart,  176. 
Auriculo- ventricular  bundle  of  His,  180. 
Automatic  acts,  410. 
Automaticity  of  muscle,  99,  231. 
Autonomic  nervous  system,  402. 
Axillary,  artery,  205. 

vein,  216,  226. 
Axis,  75. 

cylinder  process,  33,  34,  42. 
Axon,  33. 
Azygos  veins,  221. 

Bacteria,    action    of,  in  large  intestine, 
324. 

in  small  intestine,  323. 
Bartholin,  gland  of,  471. 
Base,  7. 
Basic  oxide,  7. 

Basilar  membrane  of  ear,  441,  458. 
Baths,  cold,  388. 

hot,  388. 

regulation  of  heat  by,  388. 
Biceps,  of  arm,  123. 

of  thigh,  127. 
Bicuspid,  teeth,  277. 

valve,  178,  194. 
Bile,  322,  332. 

action  of,  323. 

duct,  common,  295. 

ducts,  295,  303. 

-secreting  function  of  liver,  296. 
Bladder,  363,  373. 
Blastoderm,  27,  41. 
Blind  spot,  450. 
Blood,  154,  168. 

antibodies  in,  162,  171. 

antitoxins  in,  171. 

changes,  in  inflammation,  159,  169. 

characteristics  of,  154. 

circulation  of,   228;   and  see  Circula- 
tion. 

clotting  of,  163 ;    and  see  Coagulation 
of  blood. 

coagulability  of,  164,  171. 

composition  of,  155,  161,  168. 

defibrinated,  165. 

difference  between  lymph  and,  166. 

distribution  of,  235. 

effects  of  respiration  upon,  261,  270. 

enzymes  in,  162. 

extractives  in,  161,  162. 

functions  of,  155,  168. 

gases  in,  161,  162. 

haemoglobin,  156. 

in  urine,  370. 


INDEX 


511 


Blood  —  continued 

interchange  between  lymph  and,  167. 

internal  secretions  in,  162,  343. 

opsonins  in,  159. 

plasma,  160,  161,  170. 

-plates,  160,  170. 

proteins  in,  161. 

quantity,  154. 

rate  of  flow  of,  234. 

regeneration  of,  after  hemorrhage,  165, 

172. 

salts  in,  162. 
serum,  163. 

special  substances  in,  162. 
summary  of,  168. 
Blood-cells,  155,  168. 
red,  155,  168. 

differences  between  white  and,  160, 

170. 

function  of,  156, 169. 
life  cycle  of,  157,  169. 
number  of,  156,  168. 
white,  157,  169. 

amoeboid  movements  of,  158. 
differences   between   red   and,    160, 

170. 

function  of,  158,  169. 
life  cycle  of,  160,  169. 
number  of,  157,  169. 
varieties  of,  158,  169. 
Blood-pressure,  235,  245. 
arterial,  235,  245. 
capillary,  235. 

effect  of  respiration  on,  233. 
method  of  determining,  236,  245. 
normal  degree  of,  237,  245. 
venous,  235,  245. 
Blood- vascular  system,  173,  193. 
Blue  baby,  243. 
Bodily  heat,  384. 
distribution  of,  385. 
loss  of,  386,  393. 
production  of,  386,  393. 
regulation  of,  387,  394. 
variations  in,  389. 
Body,  back  view  of,  15. 
cavities  of,  17. 

contents  of,  17,  18. 
chemical  elements  in,  5. 
front  view  of,  14. 
human,  16,  18. 
structural  units  of,  20. 
surfaces  of,  13. 
Bone,  or  bones,  52. 
atlas,  74. 
axis,  75. 

blood-vessels  of,  56. 
calcaneum,  87. 
callus,  57. 
canaliculi  of,  55. 
cancellated,  53. 
classification  of,  60,  88. 
clavicle,  79. 


coccyx,  77. 
compact,  55. 
composition  of,  52,  59. 
dense,  53. 
depressions  of,  62. 
digits,  of  foot,  88. 

of  hand,  82. 
epistropheus,  75. 
ethmoid,  67. 
femur,  85. 

fibres  of  Sharpey,  56. 
fibula,  86. 
flat,  62. 
frontal,  65. 
functions  of,  60,  88. 
growth  of,  56. 
Haversian  canals,  55. 

system,  55. 
humerus,  80. 
hyoid,  72. 
ilium,  83. 
incus,  439. 

inferior  turbinated,  71 
irregular,  62. 
ischium,  83. 
lacrimal,  71. 
lacunas  of,  55. 
lamellae  of,  55. 
long,  60. 
lower  jaw,  72. 
malar,  71. 
malleus,  439. 
mandible,  72. 
marrow,  55. 
maxilla,  71. 
maxillary,  inferior,  72. 

superior,  71. 

medullary  canal  of,  55,  61. 
metatarsus,  88. 
nasal,  70. 
number  of,  60. 
occipital,  64. 
of  arm,  80. 
of  calf,  86. 
of  carpus,  81,  82,  89. 
of  cranium,  63. 
of  ear,  88,  439. 
of  elbow,  81. 
of  face,  70,  88. 
of  foot,  87,  88. 
of  hand,  82. 
of  head,  63,  88. 
of  heel,  87. 
of  hip,  83. 
of  instep,  88. 
of  leg,  82. 

of  lower  extremities,  82,  89. 
of  metacarpus,  82. 
of  metatarsus,  88. 
of  skull,  63. 
of  sole,  88. 
of  tarsus,  87,  89. 
of  thigh,  85. 


512 


INDEX 


Bone,  or  bones  —  continued 

of  thorax,  77. 

of  trunk,  73,  89. 

of  upper  extremities,  78,  89. 

of  wrist,  82. 

palate,  71. 

parietal,  65. 

patella,  86. 

pelvis,  83. 

periosteum  of,  56. 

phalanges,  of  foot,  88. 
of  hand,  82. 

processes  of,  62,  63. 

pubes,  83. 

radius,  81. 

regeneration  of,  56. 

ribs,  78. 

sacrum,  77. 

scapula,  79. 

sesamoid,  60. 

shin,  86. 

short,  62. 

sphenoid,  68. 

spongy,  53. 

stapes,  439. 

sternum,  77. 

structure  of,  53,  54. 

summary  of,  59,  88,  89. 

table  of,  88,  89. 

temporal,  66. 

tibia,  86. 

ulna,  81. 

upper  jaw,  71. 

varieties  of,  59. 

vertebrae,  73,  74,  89. 

vomer,  70. 

Brachial,  artery,  205. 
Brain,  410,  426  ;   and  see  Cerebrum. 

association  areas  of,  421. 

divisions  of,  412,  426. 

function,  localization  of,  419. 

membranes  of,  410. 

motor  areas  of,  419. 

sense  areas  of,  420. 

speech  areas  of,  420. 

structure  of,  411. 

summary,  426. 

ventricles  of,  417,  427. 

weight  of,  411. 

Breast  bone,  77  ;   and  see  Sternum. 
Breasts,  474,  487;    and  see  Mammary 

glands. 
Breathing,  see  Respiration,  258,  267. 

nasal,  advantages  of,  249,  267. 
Broad  ligaments  of  uterus,  468. 
Bronchi,  254,  268. 
Bronchial,  arteries,  206. 

tubes,  254. 
Bronchioles,  254. 
Brunner's  glands,  286. 
Buccal  cavity,  18,  19,  273,  298. 
Buccinator,  109. 
Bursse,  synovial,  143. 


Cajcum,  288. 
Calcaneum,  87. 
Calculi,  370. 
Calf  bone,  86. 
Callus,  57. 
Calorie,  12,  341,  342. 

large,  12,  341,  342. 

small,  12,  341,  342. 
Calyces  of  kidney,  357. 
Canal,  or  canals,  63. 

auditory,  437. 

inguinal,  121. 

semicircular,  441,  458. 
Canaliculi,  of  bone,  55. 
Cancelli,  of  bone,  55. 
Canine  teeth,  277. 
Canthus,  of  eye,  444. 
Capillaries,  173,  183,  194. 

distribution  of,  183. 

function  of,  184. 

influence  of,  on  circulation,  233. 

structure  of,  183. 
Capsule  of  Tenon,  447. 
Carbohydrates,  306,  327. 

function  of,  337,  350. 

metabolism  of,  335,  350. 
Carbon  dioxide,  263. 
Cardiac  muscle,  100. 
Carotid  arteries,  common,  203. 

external,  204. 

internal,  204. 
Carpus,  bones  of,  82,  89. 
Cartilage,  50. 

cricoid,  250. 

elastic,  47. 

hyaline,  50. 

summary  of,  58. 

thyroid,  250. 

true,  50. 

varieties  of,  50. 

white  fibro-,  50. 

yellow,  51. 
Casts,  in  urine,  370. 
Catalysis,  9. 
Cauda  equina,  404. 
Cavities,  abdominal,  18. 

buccal,  18,  19,  273,  298. 

cranial,  17. 

dorsal,  17. 

glenoid,  of  scapula,  80. 

nasal,  18,  19,  248,  267. 

of  body,  17,19.,^ 
contents  of,  19. 

orbital,  18. 

pelvic,  18. 

spinal,  17. 

thoracic,  18. 

ventral,  17. 
Cell,  or  cells,  20. 

amoeboid  movement  of,  158. 

bipolar,  32. 

differences  in,  25,  41. 

life  activities  of,  22,  40. 


INDEX 


513 


Cell,  or  cells  —  continued 

mastoid,  66. 

meanings  of  term,  20,  66.  . 

metabolism  of,  23,  335. 

nerve,  32,  42. 

prickle,  30. 

reproduction  of,  24. 

respiration  in,  22. 

summary,  40. 

wandering,  158. 
Cell-division,  24. 
Central  canal  of  cerebro-spinal  system, 

405,  417. 

Central  lobe  of  cerebrum,  417. 
Centres,  in  medulla,  412. 

nerve,  412,  427. 
Centrosome,  22. 
Cerebellum,  413,  427. 

functions  of,  414,  427. 

peduncles  of,  414. 
Cerebro-spinal  fluid,  411. 
Cerebrum,  415,  427. 

areas  of,  419. 

convolutions  of,  415,  427. 

cortex  of;  415. 

fissures  of,  415,  416,  427. 

functions  of,  418. 

lobes  of,  416,  427. 

localization  of  function  in,  419. 

sulci  of,  415,  427. 
Ceruminous  glands,  482. 
Change,  4. 

chemical,  4. 

physical,  4. 
Chemical  change,  4. 

equation,  6. 

formula,  6. 
Chemistry,  3. 

Chest,  muscles  of,  114,  135. 
Cheyne-Stokes  respiration,  270. 
Chordae  tendineae,  178. 
Choroid,  448,  461. 
Chyle,  167,  172. 
Chyme,  316. 
Ciliary  body,  448,  461. 

processes,  448,  461. 
Ciliated  epithelium,  29. 
Circle  of  Willis,  204. 
Circulation,  of  blood,  228,  244. 

changes  in,  in  inflammation,  159,  169. 

diagram  of,  229. 

factors  governing,  223,  244. 

foetal,  240,  246. 

influence  of  capillaries  on,,  233. 

influence  of  elasticity  and  extensibility 
of  arteries  on,  233. 

pulmonary,  229,  244. 

rate  of,  230. 

summary  of,  244. 

systemic,  229,  244. 
Circumduction,  95. 
Circumvallate  papillae,  434. 
Clavicle,  79. 

2L 


Climacteric,  473. 

Clitoris,  471. 

Clothing,  regulation  of  bodily  heat  by,  388. 

Coagulation  of  blood,  163,  171. 

conditions,  affecting,  164,  171. 
hastening,  164,  171. 
hindering,  164,  171. 

intravascular,  165,  172. 

value  of,  164,  171. 
Coccyx,  77. 
Cochlea,  441,  458. 
Cochlear  nerve,  442,  458. 
Coeliac  axis,  207. 
Coenzymes,  312. 
Collar  bone,  79. 
Collateral  ganglia,  401,  425. 
Collaterals,  34,  36,  42.    - 
Colon,  289. 

ascending,  289. 

descending,  289. 

transverse,  289. 
Colostrum,  476,  487. 
Columnar  epithelium,  29. 
Complemental  air,  262. 
Compounds,  3. 

inorganic,  5. 

organic,  5. 
Condiments,  340. 
Conduction,  nerve,  410. 
Condylarthrosis,  96. 
Condyles,  of  bone,  63. 

of  femur,  85. 
Conjunctiva,  445. 
Connective  tissues,  44. 

adenoid,  50. 

adipose,  48. 

areolar,  44. 

bone,  52. 

cartilage,  50. 

elastic,  47. 

fibrous,  46. 

lymphoid,  50. 

neuroglia,  50. 

reticular,  49. 

retiform,  49. 

summary  of,  57. 

varieties  of,  44. 
Constipation,  325. 
Contractility,  muscular,  100. 
Cord,  umbilical,  240. 
Corium,  140,  145,  376. 
Cornea,  448,  460. 
Coronary  arteries,  181. 

veins,  214. 

Corpora  Arantii,  179. 
Corpuscles,    blood,    155,    168;     and    see 
Blood-cells. 

Malpighian,  of  kidneys,  360,  372. 

of  Pacini,  480. 

red,  155,  168. 

renal,  360,  372. 

tactile,  378. 

white,  157,  169. 


514 


INDEX 


Corpus  callosum,  416. 

luteum,  465. 

Corti,  organ  of,  441,  457. 
Coughing,  266. 
Cowper's  glands,  480,  489. 
Cranial  cavity,  17,  19. 

nerves,  421,  428. 
Cranium,  bones  of,  63. 
Creatinin,  in  urine,  368. 
Crest,  of  bone,  63. 

of  ilium,  83. 
Cretinism,  344. 
Cricoid  cartilage,  250. 
Crying,  266. 

Crypts  of  Lieberkuhn,  286. 
Crystalline  lens,  452,  462. 
Cutaneous  membrane,  147. 

sensation,  430. 
Cuticle,  376,  390. 
Cutis  vera,  376,  390. 
Cystic  duct,  295. 
Cytoplasm,  21. 

Decidua  serotina,  483. 

vera,  483. 

Decussation  of  nerve-fibres,  412. 
Defecation,  325. 
Defibrinated  blood,  165. 
Degeneration  of  nerves,  408. 
Deglutition,  316. 
Dehydration,  9. 
Deltoid,  122. 
Dendrites,  33,  42. 
Dentine,  275. 
Derma,  377,  391. 

Descending  tracts  of  spinal  cord,  406. 
Diabetes  mellitus,  291,  337. 
Dialysis,  10,  12,  167. 
Diapedesis,  159. 
Diaphragm,  18,  19,  117. 
Diarthroses,  92,  96. 
Diastase,  320. 
Diastole,  230. 
Diet,  accessory  articles  of,  309,  340. 

regulation  of  bodily  heat  by,  387. 
Diffusion,  9. 
Digestion,  297,  304,  327. 

accessory  organs  of,  290. 

action  of  bacteria,  323. 

chemical,  311. 

in  mouth,  315. 

in  stomach,  315,  331. 

intestinal,  319,  332. 

mechanical,  310. 

necessity  for,  311. 

processes  of,  311,  329. 

summary  of,  327. 

temperature  necessary  for,  312. 
Digestive  fluids,  enzymes  in,  311. 

processes,  310,  329. 
chemical,  311. 
mechanical,  310. 

system,  271,  297. 


Digits,  of  foot,  88,  89. 

of  hand,  82,  89. 
Diploe,  68. 

Disaccharids,  as  food,  306. 
Discs,  inter  vertebral,  76. 
Discus  proligerus,  464. 
Dislocation,  95. 
Distal,  13. 
Dorsal  artery  of  foot,  213. 

cavity,  17,  19. 

surface,  13. 

Douglas,  pouch  of,  469. 
Duct,  bile,  295. 

common  bile,  295. 

cystic,  295. 

ejaculatory,  479,  488. 

hepatic,  295. 

nasal,  445. 

Stenson's,  274. 

thoracic,  187,  195. 
Ductless  glands,  343,  352. 
Ductus  arteriosus,  240. 

communis  choledocjms,  295. 

venosus,  240. 
Duodenal  glands,  286. 
Duodenum,  284. 
Dura  mater,  410. 
Dyspnoea,  264. 

Ear,  bones  of,  439. 

external,  437,  457. 

internal,  440,  458. 

middle,  438,  458. 
Ectoderm,  27,  41. 
Efferent  nerve-fibres,  34,  37,  132. 
Ejaculatory  ducts,  479,  488. 
Elastic  tissues,  47. 
Elasticity  of  muscle,  100. 
Elbow  bone,  81. 
Elements,  3,  20. 

in  human  body,  5. 
Elimination,  355,  371. 

organs  of,  355,  371. 
Embolus,  165,  172. 
Embryo,  482. 
Emulsion,  12. 
Enarthrosis,  96. 
End  arborizations,  36. 
Endocardium,  176. 
Endolymph,  440. 
Endosteum,  55,  59. 
Endothelium,  140. 
Energy,  9. 

value  of  food,  341. 
Ensiform  process,  77,  78. 
Enterokinase,  321. 
Entoderm,  27,  41. 
Enzymes,  311,  312,  330. 

in  blood,  162,  171. 

in  digestive  fluids,  311,  329. 
Epicritic  sensations,  432. 
Epidermis,  28,  376,  391. 
Epididymis,  478. 


INDEX 


515 


Epigastric  region  of  abdomen,  279. 
Epiglottis,  250,  251. 
Epimysium,  98. 
Epinephrin,  in  blood,  162. 
Epiphysis,  347,  353. 
Epistropheus,  75. 

Epithelial    tissue,    28 ;     and     see     Epi- 
thelium. 
Epithelium,  28. 

ciliated,  29. 

columnar,  29. 

functions  of,  31,  32. 

pavement,  29. 

simple,  28. 

stratified,-  30. 

summary  of,  41. 

transitional,  30. 

varieties  of,  28. 
Equation,  chemical,  6. 
Equilibrium,  nitrogen,  340,  351. 

sense  of,  443,  458. 
Erectile  tissues,  479. 
Erector  spinse  muscles,  112. 
Erepsin,  321. 
Ethmoid  bone,  67. 
Eustachian  tubes,  278,  439. 

valve,  180. 
Excreta,  355,  371. 

discharge  of,  355,  371. 
Excretion,  150,  153. 

table  of,  150,  153. 
Excretory  organs,  355,  371. 

system,  26,  41. 
Exercise,  regulation  of   bodily  heat  by, 

387. 

Exophthalmic  goitre,  345. 
Expiration,  258,  269. 
Expression,  muscles  of,  109. 
Extensibility  of  muscle,  100. 
Extension,  94. 
Extensor  muscles,  of  forearm,  124. 

of  leg,  139. 
External,  13. 

oblique  muscle  of  abdomen,  110. 

senses,  429. 
Extractives,       in       blood,       161,       162, 

170. 

Extremities,  19. 
Eye,  accessory  organs  of,  444. 

canthus  of,  444. 
%muscles  of,  133,  446,  459. 

nerves  of,  446,  460. 

pupil  of,  449,  461. 

white  of,  447. 

window  of,  448. 
Eyeball,  447,  460. 

dimensions,  447. 

muscles  of,  133,  446. 

refracting  media,  447,  460. 

tunics,  447,  461. 
Eyebrows,  444,  459. 
Eyelashes,  444. 
Eyelids,  444,  459. 


Face,  63. 

bones  of,  70. 

muscles  of,  104,  133. 
Facial  nerve,  422. 
Fallopian  tubes,  465,  485. 
Falx  cerebri,  416. 
Fascia,  or  Fasciae,  46,  98. 

deep,  47. 

lumbar,  119. 

palmar,  47. 

plantar,  47. 

superficial,  47. 
Fatigue,  103,  132,  455. 
Fats,  action  of  pancreatic  fluid  upon,  321. 

as  food,  307,  328. 

decomposition  of,  308. 

digestion  of,  321. 

function  of,  338. 

in  blood,  162,  170. 

metabolism  of,  338,  350. 
Fauces,  273,  278. 
Feces,  324. 
Female  generative  organs,  463. 

physiology  of,  472. 
Femoral,  artery,  210. 

vein,  220,  226. 
Femur,  85. 
Fenestra,  ovalis,  438,  458. 

rotunda,  438,  458. 
Fever,  390,  394. 
Fibrin,  161.  ^ 
Fibrinogen,  f61. 

in  blood,  163,  170. 
Fibro-cartilage,  elastic,  51. 

inter  vertebral,  76. 

white,  51. 

yellow,  51. 
Fibrous  tissue,  46. 
Fibula,  86. 

Filiform  papillae,  435. 
Fimbriae  of  Fallopian  tube,  465. 
Fissure,  63. 
Flavors,  340. 
Flexion,  94. 

Flexor  muscles,  of  forearm,  124. 
Fcetal  circulation,  240,  246. 
Follicles,  simple,  286. 
Fontanelles  of  skull,  69. 
Food,  action  of  bile  upon,  322. 
of  gastric  fluid  upon,  318. 
of  pancreatic  fluid  upon,  320. 
of  saliva  upon,  314. 

amount  necessary,  342,  352. 

changes  undergone  by,  in  large  intes- 
tine, 323,  332. 
in  mouth,  313,  331. 
in  small  intestine,  319,  332. 
in  stomach,  315,  331. 

classification  of,  305,  327. 

definition  of,  304. 

heat  value  of,  342,  351. 
Foot,  bones  of,  87,  88. 

digits  of,  88. 


516 


INDEX 


Foot,  bones  of  —  continued 

dorsum  of,  artery  of,  213. 

phalanges  of,  88. 
Foramen  magnum,  65. 

of  bone,  63. 

of  Monro,  418. 

ovale,  178,  240. 
Forearm,  muscles  of,  124. 
Formula,  chemical,  6. 
Fossa,  glenoid,  67. 

nasal,  248. 

of  bone,  63. 
Fovea  centralis,  451. 
Fracture,  53. 

green-stick,  53. 
Frontal  bone,  65. 

lobe  of  cerebrum,  416. 

sinuses,  66. 

Fungiform  papillae,  435. 
Funiculi,  of  nerve  fibres,  37. 

Gall-bladder,  297,  303. 

function  of,  297. 
Ganglia,  collateral,  401,  425. 

on  spinal  nerves,  408. 

sympathetic,  401,  425. 

terminal,  401,  425. 

vertebral,  400,  425. 
Ganglion,  39. 

Gases  in  blood,  161,  162,  171. 
Gaster,  299 ;  and  see  Stomach. 
Gastric,  artery,  207. 

fluid,  317,  330. 

lipase,  317. 

secretin,  317. 
Gastrin,  317. 
Gastrocnemius,  130. 
Generative  organs,  female,  463,  484. 
external,  470,  484. 
function  of,  472. 
internal,  463,  484. 
physiology  of,  472. 

male,  477,  487. 
Genioglossus,  109. 
Germinative  layer  of  skin,  376. 
Gigantism,  347. 
Ginglymus,  96. 
Gladiolus,  77. 
Glands,  147. 

accessory  thyroid,  344. 

adrenal,  345. 

Bartholin's,  471. 

Brunner's,  286. 

ceruminous,  382,  438. 

classification  of,  148. 

compound,  148. 

Cowper's,  480. 

development  of,  148. 

ductless,  149,  343,  352. 

duodenal,  286. 

intestinal,  286. 

lacrimal,  445. 

mammary,  474,  487. 


Meibomian,  444. 

of  stomach,  282. 

of  vulva,  471. 

parathyroid,  345. 

parotid,  274. 

prostate,  480. 

salivary,  274. 

sebaceous,  381,  392. 

secreting,  148. 

simple,  148. 

sublingual,  274. 

submaxillary,  274. 

summary  of,  152. 

suprarenal,  345. 

sweat,  382,  392. 

tarsal,  444. 

thymus,  345. 

thyroid,  344. 

urethral,  471. 

vulvo-vaginal,  471. 
Glenoid  cavity,  80. 

fossa,  67. 

Glisson's  capsule,  296. 
Globulins,  161. 
Glomerulus,  360. 
Glossopharyngeal  nerve,  423. 
Glottis,  251. 
Glucose,  in  urine,  369. 
Gluteus  maximus,  127. 

medius,  127. 

minimus,  127. 

Glycogenic  function  of  liver,  296. 
Glycogenolysis,  347. 
Glycosuria,  369. 
Goitre,  345. 

exophthalmic,  345. 
"Goose  flesh,"  381. 
Graafian  follicles,  464,  484. 
Green-stick  fracture,  53. 
Gristle,  50  ;  and  see  Cartilage. 
Gullet,  278,  299. 

Haemoglobin,  156. 
Hair,  379,  392. 
Hamstring  muscles,  128. 
Hand,  body  of,  82. 

bones  of,  82. 
Haversian,  canal,  54,  55. 

system,  55,  59. 
Head,  63. 

bones  of,  63. 

muscles  of,  104. 

of  bone,  63. 
Hearing,  437,  442,  457. 
Heart,  173,  193. 

auricle,  176. 

auriculo-ventricular    bundle    of    His, 
180. 

-beat,  230,  244. 
cause  of,  231. 

blood  supply  of,  181,  194. 

cavities  of,  176,  193. 

chordae  tendineae,  178. 


INDEX 


517 


Heart  —  continued 

endocardium,  175. 

murmurs,  231. 

muscle,  100,  174. 

myocardium,  174. 

nerve  supply  of,  181,  194,  232. 

orifices  of,  177,  193. 

papillary  muscles,  178. 

pericardium,  175. 

sounds  of,  231,  244. 
causes  of,  231. 

summary,  193. 

valves  of,  178,  194. 
bicuspid,  178,  194. 
function  of,  179,  194. 
influence  of,  on  circulation,  233. 
mitral,  179,  194. 
semilunar,  179,  194. 
tricuspid,  178,  194. 

ventricles,  176. 
Heat,  bodily,  384. 

centres  for,  386. 

distribution  of,  385. 

loss  of,  385. 

production  of,  384. 

regulation  of,  387,  394. 

variation  in,  389. 

where  produced,  384,  393. 
Heel  bone,  87. 
Hemophilia,  164,  171. 
Hemorrhage,  regeneration  of  blood  after, 

165,  172. 

Hemorrhoidal  artery,   superior,  210. 
Hepatic,  artery,  207,  295. 

cells,  294. 

duct,  295. 

flexure,  289. 

vein,  223. 
Hernia,  121. 
Hiccough,  265.     . 
Highmore,  antrum  of,  70. 
Hip,  bones  of,  83. 
Hippuric  acid,  368. 
Hormones,  149,  343. 
Humerus,  80. 
Humor,  aqueous,  452,  460. 

vitreous,  453,  460. 
Hunger,  433,  456. 
Hyaline  cartilage,  50. 
Hyaloid  membrane,  453. 
Hydrate,  8. 
Hydration,  8. 

Hydrochloric  acid  in  gastric  juice,  317. 
Hydrolysis,  8,  309,  311. 
Hymen,  471. 

imperf orate,  471. 
Hyoid,  bone,  72. 
Hypermetropia,  454,  462. 
Hyperpncea,  264. 
Hypertonic,  11. 

Hypochondriac  regions  of  abdomen,  279. 
Hypogastric,  artery,  210. 

region  of  abdomen,  279. 


Hypoglossal  nerve,  423. 
Hypophysis,  346,  353. 
Hypotonic,  11. 

Iced  food  or  drinks  injurious,  314. 

Iliacus,  126. 

Ileo-csecal  valve,  289. 

Ileum,  284. 

Iliac,  arteries,  210,  225. 

regions  of  abdomen,  279. 

veins,  220,  226. 
Iliopectineal  line,  83. 
Ilium,  83. 

Images,  inversion  of,  455. 
Immune  bodies,  in  blood,  162,  171. 
Impregnation,  481,  490. 

site  of,  482. 
Incisor  teeth,  277. 
Incus,  439. 

Indican,  in  urine,  369. 
Inferior  maxillary  nerve,  422. 

mesenteric  artery,  209. 

turbinated  bones,  71. 
Inflammation,    circulatory    changes    in, 

159, 169. 

Infundibulum  of  lungs,  255. 
Infusion,  intravenous,  165,  172. 
Inguinal  canal,  121. 

ligament,  119. 

regions  of  abdomen,  279. 
Inhibition,  33,  410. 
Innominate  artery,  203. 

vein,  217,  226. 
Inorganic  compounds,  5. 
Inosculation  of  arteries,  198. 
Insalivation,  313. 
Inspiration,  258,  269. 
Intercellular  substance,  44. 
Intercostal  arteries,  207. 

muscles,  115,  117. 
Interepithelial  arborizations,  36. 
Interlobular  veins,  294. 
Internal,  13. 

oblique  muscle  of  abdomen,  119. 

secretions,  149,  343. 
in  blood,  162,  343. 

senses,  429. 

Intervertebral  discs,  77. 
Intestinal  digestion,  319. 

fluid,  321. 

glands,  286. 

Intestine,    discharge    of    waste    matters 
from,  150. 

large,  288 ;  and  see  Large  intestine. 

small,  283  ;   and  see  Small  intestine. 

thick,  288 ;   and  see  Large  intestine. 

thin,  283  ;   and  see  Small  intestine. 
Intralobular  veins,  294. 
Intravenous  infusion,  165,  172. 
Inversion  of  images,  455. 
Invertase,  322. 
Ion,  7. 
Iris,  448,  461. 


518 


INDEX 


Irritability,  100. 
Ischium,  83. 
Island  of  Reil,  417. 
Islands  of  Langerhans,  291. 
Iso  tonic,  11,  165. 

Jejunum,  284. 
Joints,  90. 

ball-and-socket,  93. 

classification  of,  90. 

condyloid,  94. 

freely  movable,  92. 

gliding,  93. 

hinge,  93. 

immovable,  90. 

movements  of,  94. 

pivot,  94. 

saddle,  94. 

slightly  movable,  92. 

summary  of,  96. 

sutures,  90. 
Jugular  veins,  214,  225. 

Karyokinesis,  24  ;  see  Mitosis. 
Katabolism,  335. 
Kidneys,  356,  372. 

blood  supply  of,  361,  372. 

calyces,  357. 

capsule,  356,  358,  360. 

function  of,  362,  372. 

glomerulus,  360,  361,  362. 

Malpighian  corpuscles,  360,  372. 

matter  eliminated  by,  355. 

nerves  of,  362,  372. 

papillae,  358. 

pelvis,  357. 

pyramids,  360. 

structure,  357,  372. 

supports,  356. 

uriniferous  tubules,  358,  372. 
Kinetic  theory,  10. 
Knee-cap,  86. 

Labia  majora,  470. 

minora,  470. 
Labyrinth,  440,  458. 

bony,  440,  458. 

membranous,  440,  458. 
Lacrimal  apparatus,  445,  459. 

bones,  71. 

gland,  445. 

sac,  445. 
Lactase,  322. 
Lacteals,  188,  189,  195. 
Lactose,  476. 
Lacunae  of  bone,  55. 
Lamellae  of  bone,  55. 
Langerhans,  islands  of,  291. 
Language,  basis  of,  420. 
Large  intestine,  288,  301. 

action  of  bacteria  in,  324. 

changes  undergone  by  food  in,  323. 

coats  of,  289. 


divisions  of,  288. 

functions  of,  290. 

movements  of,  323. 

secretion  of,  324. 
Larynx,  250,  267. 
Lateral,  13. 
Latissimus  dorsi,  112. 
Laughing,  266. 
Leg,  bones  of,  82. 
Leucocytes,  158. 
Leucocytosis,  157. 
Leucopenia,  157. 
Levatores  costarum,  115,  117. 
Levator  palpebrae  superioris,  108,  444. 
Lieberkuhn,  crypts  or  follicles  of,  286. 
Ligamenta  flava,  47,  76. 
Ligaments,  46. 

annular,  99. 

inguinal,  119. 

of  uterus,  468,  469,  485. 
Ligamentum  nuchae,  111. 
Light,  perception  of,  451. 

rays  of,  in  hypermetropic  eye,  454, 462. 
in  myopic  eye,  454,  462. 
in  normal  eye,  453,  462. 
Limbs,  19. 
Linea  alba,  120. 
Lipase,  318,  321. 
Liver,  292,  302. 

discharge  of  waste  matters  by,  296. 

fissures,  293. 

functions  of,  296. 

ligaments,  292. 

lobes,  293. 

lobules  of,  293. 

lymphatics,  296. 

minute  anatomy,  293. 

nerves,  296. 

vessels,  293. 

Localization  of  brain  function,  419. 
Lower  extremities,  bones  of,  82. 

muscles  of,  124,  139. 
Lower  jaw-bone,  72. 
Lumbar  arteries,  210. 

fascia,  119. 

regions  of  abdomen,  279. 
Lungs,  254,  268. 

anatomy  of,  255. 

blood-vessels  of,  257. 

capacity  of,  262,  270. 

infundibulum  of,  255. 

lobule  of,  255. 

matters  eliminated  by,  355. 

nerves  of,  259. 
Lymph,  154,  166,  172,  239,  246. 

differences  between  blood  and,  166. 

flow  of,  239,  246. 

formation  of,  239,  246. 

function,  167,  172. 

interchange  between  blood  and,  167. 

nodes,  185,  189,  195,  196. 

sources  of,  166,  172. 

vascular  system,  185,  19b. 


INDEX 


519 


Lymphatic  duct,  right,  187,  195. 

part  drained  by,  186,  187. 
Lymphatics,  185,  187,  195. 
classification  of,  188. 
function  of,  189. 
Lymphatic  vessels,  185,  187,  195;    and 

see  Lymphatics, 
function  of,  191,  196. 
location  of,  191,  196. 
Lymph   nodules,   aggregated,  of   Peyer, 

287. 

solitary,  286. 
Lymphocytes,  158. 
Lymphoid  tissue,  50. 
Lymph  spaces,  185,  187,  195. 

Macula  lutea,  451. 
Malar  bone,  71. 
Malleolus,  external,  87. 

inner,  86. 

lateral,  87. 

medial,  86. 
Malleus,  439. 
Malpighian  corpuscles,  of  kidney,  360, 

372. 

Malpighian  layer  of  skin,  376,  391. 
Maltase,  322. 

Mammary  glands,  474,  487. 
Mandible,  72. 
Manubrium,  77. 
Marrow  of  bone,  55,  59. 
Mastication,  312. 

muscles  of,  108,  134. 
Mastoid,  cells,  66,  439. 

process,  66. 
Matter,  changes  in,  4. 

definition  of,  3. 

forms  of,  3. 

Maturation  of  sex  cells,  481. 
Maxilla,  70. 

Maxillary  bones,  70,  71. 
Meatus,  external  auditory,  437. 

of  bone,  63. 
Medial,  13. 
Median  line,  13. 

vein,  216. 

Mediastinal  arteries,  207. 
Mediastinum,  257,  269. 
Medulla  oblongata,  412,  427. 
centres  in,  412. 
functions'of,  412,  427. 
Medullary  canal  of  bone,  61. 

sheath,  34. 

Medullated  nerve-fibres,  34,  42. 
Meibomian  glands,  444. 
Membrana  tympani,  439. 
Membrane,  or  membranes,  46,  140. 

basement,  145. 

classification  of,  140. 

cutaneous   147. 

hyaloid,  453. 

mucous-  143 ;    and  see  Mucous  mem- 
branes. 


permeable,  11. 

pituitary,  248. 

Schneiderian,  248. 

semipermeable,  11. 

serous,  141 ;  and  see  Serous  membranes. 

summary  of,  150. 

synovial,  142  ;   and  see  Synovial  mem- 
branes. 
Meninges  of  brain,  410. 

of  spinal  cord,  406. 
Menopause,  473. 
Menstruation,  472,  486. 

and  ovulation,  472,  486. 

changes  in  connection  with,  473. 

purpose  of,  474. 
Mesenteric  artery,  inferior,  209. 

superior,  208. 
Mesentery,  272. 
Mesoderm,  28,  41. 
Metabolic  changes,  335. 

factors  promoting,  334. 
Metabolism,  22,  334,  349. 

changes  occurring  in,  335. 

factors  promoting,  334. 

functions  of,  334. 

of  carbohydrates,  335,  350. 

of  fats,  338,  350. 

of  proteins,  339,  351. 
Metacarpus,  bones  of,  82. 
Metaplasm,  22. 
Metatarsus,  88. 
Metric  system,  25,  491. 
Micturition,  364,  373. 

involuntary,  365. 
Milk,  composition  of,  477,  487. 

human  and  cow's,  477. 

secretion  of,  476,  487. 
Milk  sugar,  476. 
Mineral  matter  as  food,  327. 
Mitosis,  24. 
Mixtures,  4. 
Modiolus,  441. 
Molar  teeth,  277. 
Molecule,  3,  6. 
Monosaccharids,  306. 
Monro,  foramen  of,  418. 
Mons  Veneris,  470. 
Motor  areas  of  brain,  419,  428. 

nerve-fibres,  34,  37,  42,  395. 

plates,  37. 

tracts  of  spinal  cord,  406. 
Motor-oculi  nerve,  422. 
Mouth,  249,  273,  298;    and  see  Buccal 
cavity. 

changes  undergone  by  food  in,  313,  331. 

digestion  in,  315,  331. 
Mucous  membranes,  143. 

function  of,  146. 

gastro-pulmonary,  143. 

genito-urinary,  144 

structure  of,  144. 

summary  of,  151. 
Mucus,  153. 


520 


INDEX 


Muscles,  or  muscular  tissue,  97. 
adductors  of  thigh,  127. 
arrector,  of  hairs,  380. 
attachment  of,  to  skeleton,  98. 
automaticity  of,  231. 
biceps,  of  arm,  123. 

of  leg,  127. 
blood  supply  of,  103. 
buccinator,  109. 
cardiac,  100,  174. 
cells  of,  97. 

characteristics  of,  100. 
classification  of,  97,  131. 
contractility  of,  100,  102. 
contractor  of  pupil,  449. 
deltoid,  122. 
diaphragm,  117. 
dilator  of  pupil,  449. 
elasticity  of,  100. 
erector  spinse,  112. 
extensibility  of,  100. 
extensors  of  forearm,  124. 
external  oblique,  of  abdomen,  119. 
fatigue  of,  103. 
flexors  of  forearm,  124. 
gastrocnemius,  130. 
genioglossus,  109. 
glutei,  127. 
gluteus,  maximus,  127. 

medius,  127. 

minimus,  127. 
gracilis,  127. 
hamstring,  128. 
heart,  174. 
iliacus,  126. 

inferior  oblique,  of  eyeball,  107. 
insertion  of,  99. 
intercostals,  115,  117. 
internal  oblique,  of  abdomen,  119. 
involuntary,  99. 
irritability  of,  100. 
latissimus  dorsi,  112. 
lavatores  costarum,  115,  117. 
levator  palpebrae  superioris,  108,  444. 
nerves  of,  102. 
non-striated,  99. 
occipito-frontalis,  104. 
of  abdomen,  119,  136. 

action  of,  120. 
of  arm,  122. 
of  back,  111,  135. 
of  chest,  114,  135. 
of  expression,  109,  134. 
of  eyeball,  104,  446. 
of  face,  104,  133. 
of  forearm,  124. 
of  head,  104. 

of  lower  extremity,  125,  138. 
of  mastication,  108,  134. 
of  neck,  110,  134. 
of  orbit,  104,  133. 
of  shoulder,  122. 
of  thorax,  115,  136. 


of  tongue,  109,  134. 

of  trunk,  111. 

of  upper  extremity,  121,  137. 

orbicularis  oris,  109. 
palpebrarum,  444. 

orbital,  104. 

origin  of,  99. 

oxidation  of  glycogen,  103. 

pectoral,  114. 

pectoralis  major,  114. 
minor,  114. 

plain,  99. 

platysma,  110. 

posterior  femoral,  128. 

pronators,  of  forearm,  124. 

properties  of,  100. 

psoas  magnus,  125. 

quadratus  lumborum,  120. 

quadriceps  extensor,  129. 

recti,  of  eyeball,  104,  105. 

rectus  abdominis,  120. 
femoris,  129. 

sacrospinalis,  112. 

sartorius,  127. 

semimembranosus,  128. 

semite  ndinosus,  128. 

serratus  magnus,  115. 

Skeletal,  97,  98,  103 

soleus,  130. 

sterno-cleido-mastoid  ,110. 

stimuli  of,  101. 

storage  of  glycogen,  103. 

striated,  97. 

striped,  97. 

styloglossus,  110. 

summary,  131. 

superior  oblique,  of  eyeball,  106. 

supinators,  of  forearm,  124. 

tables  of,  133-139. 

tetanus  of,  102. 

to ni city  of,  100. 

trans  versalis,  120. 

trapezius,  Ml. 

triceps,  123. 

varieties  of,  97. 

vastus,  externus,  129. 
intermedius,  129. 
intcrnus,  129. 

visceral,  99. 

voluntary,  97. 
Muscular  contractility,  100. 

sense,  433,  456. 
•  system,  26,  41. 

tissue,  97  ;   and  see  Muscle. 
Muscularis  mucosse,  145. 
Myelin  sheath,  34. 
Myocardium,  174. 
Myopia,  454,  462.      . 
Myxcedema,  344. 

Nails,  379," 392. 
Nasal  bones,  70. 

breathing,  advantages  of,  249,  267. 


INDEX 


521 


Nasal  bones  —  continued 
cavities,  18,  19,  248,  267. 
duct,  445. 
fossae,  248,  267. 
Neck,  muscles  of,  110,  134. 
Nerve,  or  nerves,  abducens,  422. 
auditory,  422,  442,  458. 
-cell,  32,  42. 
centres,  38,  412. 
cochlear,  442,  458. 
cranial,  421,  428. 
degeneration  of,  408. 
-endings,  36,  399,  424. 

reaction  of,  399. 
.     facial,  422. 
-fibres,  34,  42. 

afferent,  34,  42,  132. 
decussation  of,  420. 
efferent,  34,  42,  132. 
funiculi  of,  37. 
medullated,  34,  400,  424. 
motor,  37,  42,  132. 
non-medullated,  36,  400. 
secretory,  275. 
sensory,  36,  42,  132. 
ganglia,  39,  400,  424. 
glossopharyngeal,  422. 
hypoglossal,  423. 
impulse,  398. 

direction  of,  399. 
identity  of,  399. 
nature  of,  398. 
speed  of,  399,  424. 
.stimulus  necessary  for,  399, 
inferior  maxillary,  422. 
mixed,  407. 
motor  oculi,  422. 
of  eye,  446. 
of  nose,  436. 
of  tongue,  435. 
olfactory,  421,  436. 
ophthalmic,  422. 
optic,  422. 
pathetic,  422. 
peripheral,  409. 
plexus,  37,  402,  425. 
pneumogastric,  423. 
processes,  33. 
regeneration  of,  408. 
spinal,  407,  426. 
spinal  accessory,  423. 
stimulation,  artificial,  399. 

physiological,  399. 
superior  maxillary,  422. 
tissue,  properties  of,  40,  43. 

varieties  of,  399. 
trifacial,  422. 
trochlear,  422. 
trunks,  38. 

formation  of,  37. 
Nerve-vagus,  423. 

vasoconstrictor,  182,  194. 
vasodilator,  182,  194. 


vasomotor,  182,  194. 

vestibular,  442,  458. 
Nervous  system,  21,  39,  41,  395,  423. 

autonomic,  402. 

central,  39,  400. 

interdependence  of,  403. 

divisions  of,  400,  424. 

functions  of,  423,  428. 

gray  matter  of,  38,  400. 

parts  of,  400,  424. 

peripheral,  39. 

reaction  circuit,  397. 

reflex  concept,  395. 

regulation  of  bodily  heat  by,  386. 

sympathetic,  39,  40,  400. 

synapse,  396. 

white  matter  of,  38,  400. 
Sfeucleolus,  21. 
SJeuraxon,  33. 
Neurilemma,  34,  42. 
Neuroglia,  32,  50,  58. 
Neurones,  32,  35,  42. 
Neutralizat  on,  8. 
Nipple,  474. 

Nitrogen  equilibrium,  340,  351. 
Nodes  of  Ranvier,  34,  42. 
Non-medullated  nerve-fibre,  36. 
Nose,  247,  267. 

external,  247,  267. 

functions  of,  247,  267. 

internal,  248,  267. 

nerves  of,  436. 

sinuses  communicating  with  the,  144, 

267. 
Nucleus  of  cell,  21. 

Obesity,  causes  of,  339,  350. 
Oblique  muscles,  of  eyeball,  106. 
Occipital  bone,  64. 

lobe  of  cerebrum,  417. 
Occipito-frontalis,  104. 
Odontoid  process,  75. 
Odors,  435,  457. 
(Edema,  240,  246. 
CEsophageal  arteries,  207. 
(Esophagus,  278,  299. 
Olecranon  process,  81. 
Olfactory  bulb,  437. 

nerve,  436. 

Omentum,  272,  282,  297. 
Ophthalmic  nerve,  422. 
Opsonins,  159. 
Optic  chiasm,  452. 

foramen,  452. 

nerve,  422,  446. 
Orbicularis  oris,  109. 
Orbit,  446,  460. 

bones  of,  446,  460. 
Orbital  cavity,  18,  19. 

muscles,  104,  133. 
Organ,  26,  41. 

of  Corti,  37,  441,  442. 
Organic  compounds,  5. 


522 


INDEX 


Organules,  36,  42. 

Os  coxae,  82. 

Osmosis,  12,  167. 

Osmotic  pressure,  11. 

Osseous  tissue,  52  ;   and  see  Bone. 

Ossicles  of  ear,  439,  458. 

Osteoblasts,  56. 

Otoliths,  440. 

Ovarian  arteries,  209. 

Ovaries,  463,  484. 

Overeating,  effects  of,  352. 

Oviducts,  465,  485. 

Ovulation,  472,  486. 

and  menstruation,  472,  486. 
Ovum,  472,  481,  486. 

fecundated,  development  of,  482,  490. 

segmentation  of,  482. 
Oxidation,  8. 
Oxide,  7. 

acid,  7. 

basic,  7. 
Oxyhsemoglobin,  156. 

Pacini,  corpuscles  of,  480. 
Pain,  432,  456. 
Palate,  273. 
Palate  bones,  71. 
Palmar  arch,  deep,  206. 
superficial,  206. 

fascia,  47. 
Pancreas,  290,  301. 

functions  of,  291. 

structure  of,  290. 
Pancreatic  fluid,  320. 

action  of,  upon  food,  327. 

secretion  of,  320. 
Papillae  of  skin,  377. 

of  tongue,  434,  457. 

on  mucous  membrane,  146. 
Papillary  muscles,  178. 
Paraglobulin,  161,  170. 
Parathyroids,  345,  353. 
Parietal  bones,  65. 

lobe  of  cerebrum,  416. 
Parotid  glands,  274. 
Patella,  86. 
Pathetic  nerve,  422. 
Pavement  epithelium,  29. 
Pectoral  muscles,  114 
Pectoralis  major,  114. 

minor,  114. 
Pelvic  cavity,  18. 
Pelvis,  83. 

brim  of,  83. 

false,  83. 

female,  84,  85. 

inlet  of,  85. 

male,  84. 

outlet  of,  85. 

strait  of,  83. 

true,  83. 
Penis,  479,  488. 
Pepsin,  318. 


Pericardial  arteries,  207. 
Pericardium,  141,  175. 
Perichondrium,  52. 
Perilymph,  440. 
Perineum,  471. 
Periosteum,  56,  59. 

function  of,  in  growth  of  bone,  57. 
Peripheral  nervous  system,  39. 
Periphery,  16. 
Peristalsis,  315,  319. 
Peritoneum,  141,  272. 
Peroneal  artery,  213. 
Perspiration,  382,  392. 

insensible,  383. 

quantity,  383,  392. 

sensible,  383. 

Peyer's  glands,  or  patches,  287. 
Phagocytosis,  159. 
Phalanges,  of  foot,  88. 

of  hand,  82. 

Pharynx,  249,  277,  299. 
Phrenic  arteries,  210. 
Physical  change,  4. 

sciences,  3. 
Physics,  3. 

Physiological  saline  solution,  165. 
Physiology,  definition  of,  13. 
Pia  mater,  410. 
Pinna,  437,  457. 
Pituitary  body,  346. 

membrane,  248. 
Placenta,  240. 
Plantar,  arch,  213. 

arteries,  211. 

fascia,  47. 

Plasma,  160,  161,  170. 
Platysma,  110. 
Pleura,  141,  257,  269. 
Plexus,  arterial,  198. 

nerve,  37,  402,  425. 
Pneumogastric  nerve,  423. 
Polysaccharids,  306. 
Pons  Varolii,  414,  427. 

functions  of,  414,  427. 
Popliteal  artery,  211. 
Portal  system,  223. 

vein,  223,  294. 
Position,  anatomical,  13. 
Poupart's  ligament,  119. 
Presbyopia,  454,  462. 
Pressure  sensation,  430,  432. 
Prickle  cells,  30. 
Process,  acromion,  80. 

ensiform,  77,  78. 

mastoid,  66. 

nerve-cell,  398. 

odontoid,  75. 

of  bone,  62. 

olecranon,  81. 

xiphoid,  77. 

Pronator  muscles,  of  forearm,  124. 
Prostate,  480,  489. 
Protecting  sheaths,  46,  367. 


INDEX 


523 


Proteins,  adequate,  339. 

as  food,  308,  328. 

classification  of,  309,  328. 

conjugated,  309. 

derived,  309. 

digestion  of,  308. 

function  of,  339. 

inadequate,  340. 

in  blood,  161,  170. 

metabolism  of,  339,  351. 

simple,  309. 
Prothrombin,  163. 
Protopathic  sensations,  432. 
Protoplasm,  5,  21. 
Proximal,  13. 
Psoas  magnus,  125. 
Ptyalin,  314. 
Puberty,  in  female,  472,  486. 

in  male,  480,  489. 
Pubes,  83. 
Pulmonary,  artery,  199. 

system,'  198,  224. 

veins,  200. 
Pulse,  238,  245. 

frequency  of,  239,  245. 

locations  where  it  may  be  felt,  238,  245. 

points  to  note,  in  feeling,  238,  245. 

ratio  of,  to  respiration,  239. 

variations  in,  239. 
Pupil,  of  eye,  449,  461. 

contraction  of,  449. 

dilatation,  449. 
Purin  bodies,  in  urine,  368. 
Purkinje  fibres,  189. 
Pus,  in  urine,  370. 
Pylorus,  281. 

Quadratus  lumborum  muscle,  120. 
Quadriceps  muscle,  129. 

Rachitis,  bones  in,  53. 
Radial  artery,  206. 

veins,  216. 
Radius,  81. 
Rales,  261. 

Rami  communicantes,  401,  425. 
Ranvier,  nodes  of,  34,  42. 
Reaction  circuit,  397. 
Receptaculum  chyli,  187. 
Reciprocal  reception,  96. 
Recti  muscles,  of  eyeball,  104,  105. 
Rectum,  289. 
Rectus  abdominis,  120. 

femoris,  129. 
Reflex  action,  410,  423. 

concept,  395. 
Reflexes,  classified,  398. 
Refracting  media,  452. 
Refraction,  453,  462. 
Refractive  apparatus,  453. 
Regeneration  of  blood,  165. 

of  nerves,  408. 
Reil,  island  of,  417. 


Remak,  fibres  of,  36. 
Renal  arteries,  208. 

corpuscles,  360,  372. 
Rennin,  318. 
Reproduction,  481,  489. 
Reproductive  system,  26. 
Reserve  air,  262. 
Residual  air,  262,  270. 
Respiration,  258,  267. 

abnormal  types  of,  264,  270. 

cause  of,  243,  269. 

cause  of  first,  260,  270. 

Cheyne-Stokes,  264. 

control  of,  259. 

effect  of,  on  air,  263. 

effect  of,  on  blood,  261,  270. 

effect  of,  on  blood  pressure,  233. 

effect  of,  on  lymph  flow,  240. 

external,  258,  269. 

frequency  of,  261. 

function  of,  258,  269. 

heat  regulation  by,  386. 

internal,  258,  269. 

redematous,  265. 

rate  of,  261,  270. 

ratio  of,  to  pulse,  239,  270. 
Respiratory  centre,  259,  269. 
reflex  stimulation  of,  244. 

movements,  modified,  265. 

sounds,  261. 

system,  26,  41,  250,  267,  269. 
Restiform  bodies,  414. 
Reticular  tissue,  49. 
Retiform  tissue,  49. 
Retina,  450,  461. 

layers  of,  450. 

Retroflection,  of  uterus,  467. 
Retroversion,  of  uterus,  467. 
Ribs,  78. 

Rickets,  bones  in,  53. 
Rods  and  cones,  450. 
Rotation,  94. 

Round  ligaments,  of  uterus,  469. 
Rugae,  of  stomach,  282. 

of  mucous  membrane,  145. 

of  scrotum,  479. 

of  vagina,  470. 
Rupture,  121. 

Saccule,  440,  458. 

Sacral  artery,  middle,  210. 

Sacrospinalis  muscle,  112. 

Sacrum,  77. 

Saline  solution,  physiological,  165. 

Saliva,  314. 

functions  of,  314. 

secretion  of,  313. 
Salivary  glands,  274,  298. 
Salt,  7. 

as  food,  305. 

in  blood,  161,  162,  171. 
Saphenous  veins,  external,  220. 

internal,  220. 


524 


INDEX 


Saponification,  321. 
Sarcolemma,  P8. 
Sartorius,  127. 
Scapula,  79. 
Scarpa's  triangle,  210. 
Schneiderian  membrane,  248. 
Sclera,  447,  460. 
Scrotum,  479,  488. 
Sebaceous  glands.  381,  392. 
Sebum,  381. 
Secretin,  317,  322. 
Secreting  glands,  148. 
Secretions,  149. 

external,  149. 

internal,  149. 

summary  of,  152. 

table  of,  153. 

Secretory  nerve-fibres,  275. 
Segmentation  of  ovum,  482. 
Semen,  480,  489. 
Semicircular  canals,  441,  458. 
Semilunar  valves,  179,  194. 
Semimembranosus,  128. 
Seminal  vesicles,  479,  488. 
Semitendinosus,  128. 
Sensations,  430,  455  ;   and  see  Senses. 

classification  of,  430,  455. 

definition  of,  429. 

epic ri tic,  432. 

organs  necessary  for,  429,  455. 

protopathic,  432. 

where  interpreted,  430. 
Sense  or  senses ;  and  see  Sensations. 

areas  of  brain,  420,  428. 

cutaneous,  430. 

exterior,  430,  455. 

external,  429,  455. 

interior,  430,  455. 

internal,  429,  455. 

muscular,  433. 

df  equilibrium,  443,  458. 

of  fatigue,  455. 

of  hearing,  437. 

of  hunger,  433. 

of  pain,  432. 

of  pressure,  430,  432. 

of  sight,  444,  451,  459. 

of  smell,  435. 

of  taste,  433. 

of  temperature,  430,  432. 

of  thirst,  433. 

of  touch,  430. 

visceral,  430. 
Sensory  area  of  brain,  420,  428. 

fibres,  34,  36,  42,  132. 

tracts  of  spinal  cord,  406. 
Serous  cavities,  189. 

membranes,  141,  151. 
arachnoid,  141. 
classes  of,  141. 
function  of,  141. 
of  capsule  of  Tenon,  141. 
of  cavities,  141. 


of  cerebrospinal  axis,  141. 
of  vascular  system,  141. 
proper,  141. 

secretion,  151. 

Serratus  magnus  muscles,  115. 
Serum,  171. 

albumin,  161,  170. 
Sesamoid  bones,  60. 
Sharpey,  fibres  of,  56. 
Sheath,  myelin,  34. 
Shin-bone,  86. 
Shoulder  blade,  79. 

muscles  of,  112,  115. 
Sighing,  265. 
Sight,  444,  459. 
Sigmoid  flexure,  289. 
Simple  epithelium,  28. 
Sinews,  46. 

Sino-auricular  node,  180. 
Sinuses  communicating  with  nose,    144, 
.267. 

of  bone,  63. 

of  head,  70. 

venus,  of  skull,  214. 
Sinusitis,  70. 
Skeletal  muscles,  97,  98. 

system,  26. 
Skeleton,  60. 
^attachment  of  muscles  to,  98. 

divisions  of,  63. 
Skin,  376,  391. 

appendages,  379,  391. 

blood-vessels  of,  378,  391. 

discharge  of  waste  matters  by,   383, 
384. 

functions  of,  376,  391. 

heat  regulation  by,  385. 

layers  of,  376,  391. 

nerves  of,  378,  391. 

summary,  391. 
Skull,  63. 

as  a  whole,  68. 

bones  of,  63. 

diploe  of,  68. 
Small  intestine,  283,  300. 

action  of  bacteria  in,  323. 

changes  undergone  by  food  in,  319. 

coats  of,  284. 

digestion  in,  319,  332. 

divisions  of,  284. 

functions  of,  288. 

glands  of,  286. 

lymph  nodules  of,  286. 

movements  of,  319. 
Smell,  435,  457. 

necessary  conditions  for,  435,  457. 
Sneezing,  266. 
Sobbing,  266. 
Soleus,  130. 
Solute,  12. 
Solution,  8. 

physiological  saline,  165. 
Solvent,  12. 


INDEX 


525 


Speaking,  266. 
Specific  gravity,  9. 
Speech  areas  in  brain,  420. 
Spermatic  arteries,  208. 

cord,  479,  488. 

Spermatozoon,  478,  481,  490. 
Sphenoidal  fissure,  446. 
Sphenoid  bone,  68. 
Sphygmomanometer,  236. 
Spina  bifida,  77. 
Spinal-accessory  nerve,  423. 
Spinal  canal,  17,  19,  404. 
cord,  403,  426. 

central  canal  of,  405. 
functions  of,  410,  426. 
membranes  of,  406,  426. 
section  of,  405. 
structure  of,  404,  426. 
tracts  of,  406. 
ganglia,  401. 
nerves,  407,  426. 

degeneration  of,  408. 

distribution  of  terminal  branches  of, 

409. 

ganglion  on  dorsal  root  of,  408. 
regeneration  of,  408. 
roots  of,  407. 
Spinous  processes,  of  bone,  63. 

of  ilium,  83. 
Spleen,  347,  354. 
Splenic  artery,  207. 

flexure,  289. 
Sprain,  95. 
Stapes,  439. 

Starch,  action  of  saliva  on,  314. 
of  pancreatic  fluid  on,  320. 
Steapsin,  321. 
Stenson's  duct,  274. 
Sterno-cleido-mastoid  ,110. 
Sternum,  77. 
Stimulants,  340. 
Stimuli,  muscular,  101. 

nerve,  399,  424. 
Stomach,  280,  299. 
blood-vessels  of,  283. 
coats  of,  282. 
component  parts,  282. 
curvatures,  282. 
digestion  in,  315,  331. 
functions  of,  283. 
glands  of,  282. 
nerves  of,  283. 
openings,  281. 
peristaltic  action  of,  316. 
Stratified  epithelium,  30. 
Styloglossus,  110. 
Subarachnoid  space,  407. 
Subclavian  arteries,  205. 

veins,  216,  226. 
Subcutaneous  tissue,  378. 
Sublingual  glands,  274. 
Submaxillary  glands,  274. 
Succus  entericus,  321. 


Sucrase,  322. 
Sugar,  306. 

in  blood,  162,  170. 

regulating  centre,  336. 
Summation,  33. 
Superior  maxillary  nerve,  422. 
Superior  mesenteric  artery,  208. 
Supinator  muscles,  of  forearm,  124. 
Suprarenal  arteries,  207. 

capsules,  345,  353. 
Sutures,  90,  96.  ' 

coronal,  90. 

frontal,  92. 

lamboidal,  90. 

of  skull,  91. 

sagittal,  90. 
Swallowing,  314. 

Sweat,  382  ;   and  see  Perspiration. 
Sweat-glands,  382,  392. 
Sylvius,  aqueduct  of,  418. 
Sympathetic  ganglia,  401,  425. 

system,  40,  400,  425. 

interdependence  of,  403. 
Symphysis,  92,  96. 

pubis,  83. 
Synapse,  396. 
Synarthroses,  90,  96. 
Synchondrosis,  92,  96. 
Syndesmosis,  92,  96. 
Synovia,  142. 

Synovial  membranes,  93,  142. 
articular,  142. 
bursal,  143. 
function  of,  143. 
vaginal,  142. 
System,  41. 
Systole,  230. 

Tactile  corpuscles,  37,  378. 
Tarsal  cartilages,  444,  459. 

glands,  444. 

Tarsus,  bones  of,  87,  89. 
Taste,  433,  456. 

buds,  433,  456. 

necessary  conditions  for,  433. 

organ  of,  433,  456. 

sense  of,  433,  456. 
Taste  buds,  433,  456. 
Tears,  445. 
Teeth,  275,  298. 

function  of,  277. 

permanent,  276. 

temporary,  276. 

Temperature,    necessary    for    digestion, 
314. 

sense  of,  432. 

subnormal,  390. 

variations  in,  389,  390,  394. 
Temporal  bones,  66. 

mastoid  portion  of,  66. 
petrous  portion  of,  66. 
squamous  portion  of,  66. 

lobe  of  cerebrum,  417. 


526 


INDEX 


Tendo  Achillis,  130. 
Tendons,  46,  98. 
Tenon,  capsule  of,  447. 
Terminal  ganglia,  401,  425. 
Testes,  477,  488. 

descent  of,  478. 
Testicle,  477  ;   and  see  Testes. 
Tetanus  of  muscle,  102. 
Thigh,  adductor  muscles  of,  127. 

bone,  85. 
Thirst,  433,  456. 
Thoracic  cavity,  18,  19. 

duct,  187,  195. 

parts  drained  by,  186,  187,  195. 
Thorax,  76,  77. 

bones  of,  77. 

muscles  of,  115,  136. 
Thrombin,  163. 
Thrombus,  165,  172. 
Thymus,  345,  353. 
Thyroid,  accessory,  344. 

cartilage,  250. 

foramen,  83. 

gland,  344,  352. 
Tibia,  87. 
Tibial  arteries,  211. 

veins,  218. 
Tidal  air,  262. 
Tissue,  or  tissues,  26,  41. 

adenoid,  50. 

adipose,  48. 

areolar,  44. 

cartilage,  50. 

classification  of,  27. 

connective,   44 ;     and  see   Connective 
tissues. 

definition  of,  26. 

elastic,  47. 

epithelial,    28;      and     see     Epithelial 
tissue. 

fibrous,  46. 

lymphoid,  50. 

muscular,  97  ;  and  see  Muscle. 

nerve,  32,  40 ;   and  see  Nerve. 

neuroglia,  50. 

origin  of,  27. 

osseous,  52 ;   and  see  Bone, 

reticular,  49. 

retiform,  49. 
Tone,  arterial,  182. 
Tongue,  274,  280,  434,  457. 

muscles  of,  109,  134. 

nerves  of,  435,  457. 

papillae  of,  434,  457. 

sensations  in,  435,  457. 
Tonicity  of  muscle,  101. 
Tonsils,  273,  298. 
Torticollis,  111. 
Touch,  sense  of,  430,  432. 
Trachea,  253,  268. 
Transference  of  impulses,  410. 
Transitional  epithelium,  30. 
Trans  versalis,  120. 


Transverse  fissure  of  cerebrum,  416. 

Trapezius,  111. 

Triceps,  123. 

Tricuspid  valve,  178,  194. 

Trifacial  nerve,  422. 

Trochanters  of  femur,  85. 

Trochlear  nerve,  422. 

Trochoides,  96. 

Trunk,  bones  of,  73",  89. 

muscles  of,  111. 
Trypsin,  320. 
Tubercle  of  bone,  63. 
Tuberosity  of  bone,  63. 
Tunics  of  eye,  447,  460. 
Tympanum,  438. 

ossicles  of,  439. 

Ulna,  81. 

Ulnar  artery,  206. 

veins,  216. 
Umbilical  cord,  240. 

^region  of  abdomen,  279. 
Under-nutrition,  252. 
Upper  extremities,  bones  of,  78,  89. 

muscles  of,  121,  137. 
Upper  jaw-bones,  71. 
Urea,  296,  335,  367. 
Ureters,  363,  373. 
Urethra,  female,  364,  373. 

jmale,  480,  489. 
Urethral  glands,  471. 
Uric  acid,  368. 
Urine,  365,  374. 

abnormal  constituents  of,  369. 

amount  of,  366,  374. 

composition  of,  367. 

excretion  of,  364. 

reaction,  366. 

retention  of,  365,  374. 

secretion  of,  362,  372. 

specific  gravity,  366. 

.suppression  of,  365,  374. 

toxicity  of,  371. 
Uriniferous  tubules,  358,  372. 
Uterine  artery,  210. 
Uterus,  463,  466,  485. 

blood  supply  of,  467,  485. 

cervix,  466. 

changes    in,    following    impregnation, 
466,  482. 

coats  of,  467. 

divisions  of,  466, 485. 

function  of,  469. 

fundus,  466. 

ligaments  of,  468,  485. 

os,  466. 

position  of,  467. 

structure  of,  467. 
Utricle  of  ear,  440,  458. 
Uvula,  273. 

Vagina,  463,  469,  485. 
Vagus  nerve,  423. 


INDEX 


527 


Valve,  or  valves,  Eustachian,  180. 

ileo-ca3cal,  289. 

of  heart,  178,  194,  233. 

of  veins,  184. 

Valvular  conniventes,  145,  285. 
Vasa  vasorum,  182,  194. 
Vascular  system,  26,  41,  154,  168,  195, 
201. 

changes  in,  at  birth,  243,  246. 
Vas  deferens,  478, 488. 
Vasoconstrictor  nerves,  182,  195,  412. 
Vasodilator  nerves,  182, 195, 412. 
Vasomotor  centres,  412. 

jierves,  182,  195,  412. 
Vastus  externus,  129. 

intermedius,  129. 

internus,  129. 
Veins,  173,  184,  194,  213,  225. 

axillary,  216,  226. 

azygos,  221,  227. 

basilic,  216. 

cava,  inferior,  220. 
superior,  217. 

cephalic,  216. 

coronary,  214. 

deep,  213. 

femoral,  220,  226. 

hepatic,  223,  295. 

iliac,  common,  220,  226. 
external,  220,  226. 
internal,  220,  226. 

influence  of,  on  circulation,  223. 

innominate,  217,  226. 

interlobular,  294. 

intralobular,  294. 

jugular,  external,  214,  225. 
internal,  214,  225. 

median,  216. 

popliteal,  211. 

portal,  223,  294. 

portal  system,  223,  227. 

pulmonarv,  200. 

radial,  216. 

saphenous,  external,  220. 
internal,  220. 

structure  of,  184. 

subclevian,  216,  226. 

superficial,  213,  215. 

systemic,  214. 

thoracic,  217. 

tibial,  anterior,  213. 
.posterior,  211. 

ulnar,  216. 

valves  of,  184. 
Vena  cava  inferior,  218,  220,  226. 

superior,  214,  217,  225. 
Venae  comites,  214. 
Ventilation,  263,  270. 
Ventral  cavity,  17,  19. 


Ventral  surface,  13. 

Ventricles,  of  brain,  417,  418,  427. 

of  heart,  176. 
Venules,  183. 
Vermiform  appendix,  289. 
Vernix  caseosa,  382. 
Vertebra,  74,  75. 

false,  74. 

number  of,  74. 

regions  of,  74. 

true,  74. 
Vertebral  artery,  204. 

column,  73. 

abnormal  conditions  of,  77. 
bones  of,  74,  75. 
curvatures  of,  75,  77. 
structure  of,  75. 

ganglia,  400,  425. 
Vesicles,  seminal,  479,  488. 
Vesicular  follicles  of  ovary,  464. 
Vestibular  nerve,  442,  458. 
Vestibule,  of  ear,  440,  458. 
Villi,  146,  285. 
Viscera,  17. 
Visceral  muscles,  99. 

sensations,  430,  455. 
Viscus,  17. 

Visual  apparatus,  444. 
Vital  capacity,  262. 

centres,  412. 
Vitamines,  343,  352. 
Vitreous  humor,  453,  462. 
Vocal  cords,  251. 
Voice,  252,  268. 

difference  between  that  of  male  and 

Jemale,  252. 
Vomer,  70. 
Vomiting,  315. 
Vulva,  470. 

glands  of,  471. 
Vulvo-vaginal  glands,  471. 

Wandering  cells,  158. 

Waste  products,  162,  170,  355,  371. 

discharge  of,  355,  371. 
Water,  as  food,  305,  327. 
Wharton's  jelly,  241. 
Willis,  circle  of,  204. 
Windpipe,  253. 
Wisdom  teeth,  277. 
Wrist,  bones  of,  82. 
Wry  neck,  111. 


Xiphoid  process,  77,  78. 

Yawning,  265. 
Yellow  spot,  451. 

Zygote,  27. 


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Books  not  returned  on  time  are  subject  to  fines  according  to  the  Library 
Lending  Code. 

Books  not  in  demand  may  be  renewed  if  application  is  made  before 
expiration  of  loan  period. 


10m-7,'59(A3819h4)4128 
ft 


